Carbon Trust Voltage Management - Ctg045

 

Technology guide

Voltage management An introduction to technology and techniques

enter

 

Contents

Understanding voltage management

2

Evaluating the potential for voltage management

How the need for voltage

A procedure to evaluate the potential

management arises

for savings

Understanding your load

5

What are voltage dependent and voltage

Calculating the energy savings

13

16

A worked example

independent loads?

Glossary Voltage manageme management nt techn techniques iques Techniques to mitigate the impact of high supply voltages

10

21

 

Voltage management 1

Foreword This document is designed to answer your questions on voltage management. It also explains how you can save both energy and money by making sure your electricity supply is set at an optimal level across your site. MENU

It is aimed particularly at the operators of larger

Voltage management is just one of a number

non-domestic premises, which typically have a three-phase electricity supply.

of energy management technologies. Before you commit to the costs involved, you should

We introduce the concept of voltage ‘dependent’ and voltage ‘independent’ loads and establish a step-by-step procedure to help you estimate the energy and cost saving potential of voltage management.

compare the benefits of installing voltage management equipment with those of alternative energy efficiency projects that remove voltage dependent loads and break the relationship between site energy demand and the supply voltage. You may also want to consider the impact the two types of project have on each other, as you’ll need to decide on the best order in which to implement them.

Further information If you’re thinking about installing voltage management equipment, this guide can help you understand the opportunity and evaluate the possible savings. To weigh up the advantages of alternative projects, such as changing lighting equipment or installing variable speed drives, you may want to consult other Carbon Trust publications, such as CTV021 Lighting Technology Overview  Overview  and CTG006 Variable Speed Drives Technology Guide

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Voltage management 2

Understanding voltage management

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What is voltage management?

If your site is being supplied with electricity at a

minimising consumption while remaining

Voltage management is an umbrella term

higher voltage level than you need, you could be wasting energy and money, and be responsible

within the operating conditions specified by the equipment manufacturer.

covering various distinct technologies, including voltage optimisation, voltage stabilisation, voltage regulation, voltage

for greater emissions than necessary. This is where voltage management can help.

by certain loads is proportional to the square of

power optimisation, or voltage reduction.

Electrical equipment can sometimes

the voltage. A supply voltage in excess of the

In the context of this document, we’ve used

consume more power at higher voltages.

nominal 400/230V may result in excessive excessive

the term to maintain an impartial position

Voltage management reduces the voltage

energy consumption.

with regard to equipment selection.

of the electricity supplied to equipment,

How does it work? The basic principal of all voltage management equipment is to reduce the voltage level

The ratio of primary to secondary windings of these electrical transformers is set to provide the desired level of voltage reduction.

from that of the incoming supply. To achieve

Whilst there are a range of manufacturers and

this change in voltage level, an electrical

various specifications of voltage management

transformer is required.

equipment, it is this fundamental device which sits at the heart of the equipment.

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Basic electrical laws mean the power required

 

Voltage management 3

Why might my supply voltage be higher than necessary necessar y?

electrical equipment to be supplied in Europe.

Until 1995, the statutory supply specification in

Equipment that meets this standard bears the mark and is designed to operate with a

the UK was 415/240V ±6% (i.e. phase voltage

nominal supply of 230V.

(Vp) within the range 226-254V). The vast majority of the electrical distribution network has been in place for many years and was designed MENU

to deliver electricity within this range. There are many sites across the UK where the phase

207–253V (current guidance from DECC suggests this will happen in the UK during

the local electricity supply anywhere in Europe.

400/230V+10% -6%. This remains the current UK position today. To simplify the market for electrical equipment

all Europe supply 230V ±10%

254V 253V

Therefore in the UK, where supply voltages have historically been higher, equipment made for

UK

240V

European markets is often used at a higher voltage than it is optimised for. As a result the UK EU

equipment may be consuming more energy than is necessary. The following diagram illustrates

further, the European Union has introduced the

the past and proposed voltage levels in the UK

Low Voltage Directive Directive (LVD) 2006/95/ EC to

and the EU.

regulate the normal operating voltage of

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Planned harmonised EQS

UK supply 240V ±6% EU supply 220V (variable tolerance)

at 400/230V±10%, i.e. Vp within the range

Europe has been 380/220 volts with a typical

supply specification in the UK changed to

Historic arrangements (pre 1995)

will harmonise supply voltages across Europe

2011/12). This means any piece of equipment with the mark can be safely operated on

levels were taken in 1995 when the statutory

voltages across the EU 

Electricity Quality and Supply Regulation Regulations s (EQS)

voltage is normally in excess of 240V. Historically the supply voltage in mainland tolerance of ±6%. Steps to harmonise voltage

Figure 1 Impact of harmonisation of supply

Note Electricity generation transmission and distribution is based on a three-phase alternating current (A (AC) C) system. For low voltage supplies the phases are connected in a ‘star ’ arrangement are delivered using four wires – each of the three phases and the ‘neutral’ point between them. The The nominal supply voltage in the UK is currently 400/230v, which means the voltage between the phases is 400V (often called line voltage), while the voltage between each of the phases and the neutral point is 230V often called phase voltage). In order to cope with the geographic layout of electricity   distribution networks and the daily changes change s in electricity demand, electricity distribution network operators are allowed to provide phase voltages within the range 230v +10%/-6% i.e. between 216V and 253V (moving to 230V ±10%).

230V

226V

EU

220V

  207 V

 

Voltage management 4

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How does voltage management work?

irrespective of the supply voltage. They can

The theory of energy saving by voltage

Other loads, such as electric motors, are partially

management relies on simple electrical

voltage dependent. For a fixed speed motor,

formulae, which provide a relationship between

the power demanded by the load on the output

Electrical equipment is designed to operate

electrical power consumption and voltage

shaft is often independent of supply voltage,

with an electricity supply that is within the

for a constant resistance.

but some of the losses which will result from

range specified on its name plate. If the

operating the motor inefficiently are voltage

supply voltage is less or more than

dependent. The change in power demand for

specified, the equipment may not operate

a one per cent change in supply voltage will therefore be between zero and theoretically two

correctly and could switch itself off, with possible safety implications.

Power demand (kW) can be expressed as a function of voltage:

Power =

Voltage 2  Resistance 

 

This means that for a simple linear resistive load the power consumed is proportional to the square of electricity supply voltage. Therefore the higher the supply voltage, the higher the energy consumption. Equipment that displays this characteristic characteris tic can be described as ‘voltage dependent’. With a simple linear resistive load, a one per cent increase in supply voltage will cause a two per cent increase in power demand.

be considered ‘voltage independent’.

per cent. The exact proportion depends on the motor construction and its operating conditions.

When changing electricity supply voltages across a site, you will need to make sure

Electricity supply companies charge for the

that the supply is at an appropriate level. It

energy supplied, measured in kilowatt-hours

shouldn’t be so low that your equipment is

(kWh). These reflect the power consumed

supplied with a voltage lower than its rating,

(kW) and hours of operation:

nor so high that you consume unnecessary

Energy = Power x Time  

amounts of energy.

To understand how much energy and cost you

Some sites may still have older equipment

might save through voltage management, you

designed to operate on a supply voltage of

need to understand what proportion of your

415/240V ±6%. This will need to be

electrical load is voltage dependant, what

identified and taken into account in any

However, there are many different types of

proportion is voltage independent and the

voltage management project.

electrical load and most are not simple linear

number of hours each type of load operates

resistive. Modern electronic control equipment

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Safety warning – voltage management is not simply reducing voltage

such as that used in ICT and high frequency

for. The section “Understanding your load” explains in more detail how to assess which

lighting is designed to give a fixed output voltage

category your equipment falls into.

 

Voltage management 5

Understanding your load To determine whether voltage management could reduce your energy consumption, you will need to understand how much of the electrical equipment at your site is voltage dependent, and what proportion of your energy consumption that represents. MENU

If a high proportion of electrical energy at your

To help access the potential for voltage

site is consumed by equipment where the power demand is to some degree voltage

management we need to categorise electrical equipment as either voltage dependent or

dependent, voltage management should

voltage independent. These two groups are

reduce your consumption. But if your electrical

defined below.

consumption is mainly made up of voltage independent loads, you’re not likely to be able to save much energy through voltage

Voltage dependent

Example: tungsten filament lamp An ordinary 40W tungsten filament lamp is a voltage dependent load. If the lamp is supplied at 230V, it is designed to draw 40W of power. Over eight hours it will consume 0.32 kWh. The same lamp, supplied

management.

A voltage dependent load is an electrical device

at 242V, will draw over

It can be difficult to tell whether or not a

whose power consumption varies with the voltage being supplied to it.

44W of power and in the same eight hour

specific item of electrical equipment is voltage dependent and close inspection will usually be needed. However, the following guidance should help.

period consume 0.35 kWh – ten per cent more.

Note: For tungsten filament lamps, light output is also proportional to voltage. HELP

 

Voltage management 6

Voltage independent

Relationship between power and energy

A voltage independent load is an electrical device whose power demand, within its

In considering the energy efficiency and

designed operating range, is independent

energy cost aspects of voltage management,

of supply voltage.

it is important to understand the relationship between power and energy. Electricity suppliers

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Example: Power supplies for ICT equipment A power supply unit, such as those for

bill us for the energy supplied. This will depend on the level of power needed and the length of time the equipment operates for.

The examples given here are intended to illustrate clearly the concept of voltage dependent and voltage independent loads and the relationship between power and energy. In practice most devices are more complex and their overall power demand will have multiple components that could be either voltage dependent or voltage independent. This is particularly true in the case of electric motors, whose construction, application, duty,

laptop computers, is designed to give a fixed voltage output regardless of the

For some systems with feedback control, often as simple as a thermostat, the amount of energy

efficiency and size can all influence the overall operating efficiency and the degree to which

supply voltage, allowing them to be used

delivered remains the same, whatever the

it is voltage dependent. Figure 2 on the following

internationally. A typical unit gives a fixed

supply. As a result the system is effectively

pages discusses the voltage dependency of

output of 20V with a nominal input voltage

voltage independent even if the principle device

many common load types.

of between 100-240V. The power supply to

has voltage dependent characteristics.

the computer is fixed, irrespective of the supply voltage to the power supply unit. The total energy demand of the computer and power supply will not change if the supply voltage varies.

However, bringing water to boiling point takes

Example: electric kettle A traditional electric kettle with a resistive element is a simple resistive load. Like a tungsten light bulb, it will consume more power if the supply voltage is higher than the nominal supply voltage.

the same amount of energy, whatever the voltage. If the voltage is higher the kettle will just take less time to reach boiling point and switch off sooner. The fact that the kettle is thermostatically thermostatically controlled controlled means that it is, in practice, voltage independent.

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Voltage management 7

Figure 2: What types of equipment are voltage dependent? 

Load t ype

Are they voltage dependent?

Incandescent lamps

YES – Incandescent lamps (or bulbs) are a source of lighting where an electrical current runs through a filament that emits visible light. The most common types of incandescent lamps are standard tungsten filament, tungsten halogen and reflector lamps. All three of these are voltage dependent loads. Reducing the supply voltage to these lamps will result in a directly proportional reduction in power consumption. However, lower voltage and power will reduce the light output.

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Fluorescent lamps –

YES – An electrical ballast is required to strike (ignite) a fluorescent lamp. In older types an inductive (or magnetic) ballast is used. Simple magnetic ballasts provide an unregulated supply to the lamp with

inductive ballast

inductive and resistive impedance. In this arrangement the power consumed is proportional to the

(also known as switch start)

Metal halide/  SON lamps

supplied voltage. However, lower voltage and power may reduce the light output. Rated light output is achieved within ±3% of 230V design voltage.

Typically T8/T12

POSSIBLY  –  – These types of lamps have ballasts which can either be inductive or electronic. As per fluorescent lamps, depending upon the type of ballast, they can be either voltage dependent or voltage independent. The lighting supplier should be contacted to decide the type of ballasts you have and to determine their voltage dependency.

Fluorescent lamps –

supplied frequency. This leads to improved efficiency in the production of light but also means they are

electronic ballast

voltage independent1.

NO – Modern fluorescent ballasts are electronically controlled to provide voltage at a higher than

(also known as high frequency)  Typically T5 1 Electronic

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ballasts are usually classified into those with either “passive” or “active” “active” front ends. Those with passive front ends use discrete electronic components whilst those with active front ends use integrated circuits. In either case the process of conversion from mains frequency to a higher frequency result in the power demand being voltage independent.

 

Voltage management 8

L oa d t y pe

Are they voltage dependent?

LED lamps

NO – LEDs have the same power demand, regardless of supply voltage, so energy consumed does not vary with voltage.  voltage. 

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Motor loads (Uncontrolled)

YES, IN MANY CASES – Most motors in use today are asynchronous induction motors. Large (>20kW) induction motors have low losses. When operating within 70-90 per cent of their rated output they are very efficient (as high as 95 per cent), and are effectively voltage independent. However, this is an ideal position. Most motors in use today are of a smaller rating and have higher losses making them less efficient. Many of these motors are oversized for their application and often operate for all or much of the time at partial load, which leads to increased losses. It is these losses which lead to a larger proportion of a motor’s power demand being voltage dependent. If motor loads form a significant part of your total site load, you should complete a detailed technical evaluation into the savings potential.

Motor loads controlled by variable speed drive (VSD)

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NO – no additional energy savings are possible through the reduction of supply voltage.

 

Voltage management 9

Load t ype

Are they voltage dependent?

Process loads

POSSIBLY  –  – Process loads are generally electronically controlled to ensure that processes operate correctly. Most of the energy consumed in process plant will usually be by motors and heating. The potential for energy savings through voltage management is therefore dependent on how loads are controlled. You will need to seek specialist advice to assess the likely benefits of applying voltage management to process loads.

Electric heating

PROBABLY NOT – Electric heating is a resistive load and as such a higher supply voltage will result in an increase in power demand.

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However like the electric kettle (page 6), the method of control is critical to whether energy consumption increases with higher voltages. Where temperature controllers, such as thermostats, are installed and are set correctly, energy consumption will not change with an increased supply voltage. Instead instantaneous power demand will be higher and heaters will warm up quicker.

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Electronic loads and information and computer technology

power supplies, mobile phone chargers and office equipment can accept a wide range of input voltages

(ICT)

savings through voltage management are therefore negligible.

NO – Most electronic (i.e. low power) equipment is designed for world markets. For example computer while operating with fixed DC voltages. The majority of electronic equipment relies on regulated power supplies, which consume the same energy over a wide range of input voltages. The potential energy

 

Voltage management 10

Voltage management techniques MENU

Once you have determined if you can save by managing the supply voltage, you have three broad options available: •

•

voltage, regardless of load conditions, through continuous adjustment.

introduced into an electrical supply, there can be some secondary power quality benefits in

specific solution).

section. The device which suits you is best

Adjust or modify incoming electrical

Replace voltage dependent loads.

Install voltage management equipment There are two types of voltage management equipment:

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When voltage management equipment is

Your choice will depend on a number of factors,

supplied at high voltage only).

•

variable ratio which provides a constant

Install voltage management equipment  (this can be a site-wide or technology

supply infrastructure (applies to sites

•

•

fixed ratio which provides a fixed reduction at all times e.g. 10 per cent

as discussed in the Practical considerations  determined on a site-by-site basis through a technical and financial appraisal process.

addition to the managed voltage. The operation of electrical equipment can be influenced by power quality issues such as harmonics, phase imbalance, power factor, and transients. Improvement of these issues may provide some further modest energy savings, however the

Consider whether it makes sense to apply voltage management across your whole site.

magnitude of such savings is unlikely to have a significant impact on the business case for

Products are available to manage voltage for

investing in voltage management equipment.

specific loads and c an be installed downstream

A thorough analysis of power quality is required

of your main electrical incomer. These devices

to substantiate or verify savings and if your

can be a useful alternative to the site-wide

site has noticeable power quality issues you

approach if only specific systems, such as

should seek independent technical advice.

lighting, can benefit from voltage management.

Depending on the nature and severity of the problems a dedicated power quality solution may be required.

 

Voltage management 11

Adjust or modify incoming electrical supply infrastructure If your site is supplied at high voltage and you own the high voltage to low voltage transformer, you have a number of options to manage your voltage level.2

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Tap down an existing transformer Sites that are supplied at HV typically have one or more transformers to step voltage down to LV. Most transformers have tap changers installed to allow for manual ratio adjustment controlling site voltage. Tap changers typically offer a range of ±5% either in one per cent or

and contact your local electricity company to

range, low loss or super low loss equivalent

de-energise the transformer and make the

designed to deliver a nominal 230V could be

adjustment.

a highly cost effective option.

Replace existing HV/LV transformer(s) (e.g. replace replac e 11,000/41 1,000/415V 5V with 11,000/380V)

Energy savings from reduced transformer losses

It is likely that you have a transformer that is

can be achieved through replacement of

designed to provide a nominal phase voltage of 240V. If so, you could consider replacing this

a standard loss 1000kVA Transformer with a super low loss equivalent. (Additional

equipment with a unit offering a nominal voltage

savings will be seen where secondary

of 230V which would operate satisfactorily

voltages can be reduced.)

down to 207V.

Annual energy savings of close to £4,000

In this instance these savings are attributed to a reduction in two types of losses:

2.5% steps. The maximum reduction is limited

If the transformer has been on site for some

by the range of the tap changer and its existing

time, it could also have higher losses than a

position.

modern equivalent. It may also have a greater

Tapping down an existing transformer is a low

capacity than you currently need, along with a standard range of adjustment that would not

19% of savings. ii.Variable, dependent on load, copper loss,

allow it to benefit from the new voltage

accounting for 81% of savings.

cost option which can lead to a quick reduction in energy use. While it may not deliver maximum savings, it is certainly worth checking that your

harmonisation.

i. Fixed core or iron loss, accounting for

NB: Assumes transformer is permanently

transformer hasn’t been left in one of the

A thorough review of your existing

energised throughout the year and has a

‘higher’ settings. Usually tap changers are

transformer(s), power demand and transformer

75% loading and an electricity.

‘off-load’, which means that you will need to

ratings may show that changing the

engage a senior authorised electrical engineer

transformer(s) for correctly rated, wider tap

Click here to view Further transformer loss data.

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2 Note: Some sites take supply at low voltage but the DNO has the transformer that is dedicated to that site. In t his instance it would be worthwhile for the site operator to approach the DNO with regards to tapping down the transformer.

 

Voltage management 12

Replacement of voltage dependent loads Many voltage dependent loads are typically less efficient than voltage independent loads. An

Replacing motors or fitting drives may result in

motors are causing unnecessary energy

much bigger savings for the individual motor

demand, you have a number of options:

than can be delivered through at-source voltage

•

If a motor has a constant partial load it makes

example would be fluorescent lighting, where

sense to review the size of the motor and

you can improve efficiency by up to 40 per cent

replace it with one that matches the load.

by changing from an older switch start ballast MENU

If partially or variably loaded and/or uncontrolled

fitting to a modern high-frequency

fitting 3 or

•

and fans, excellent savings can be made

LED. If older voltage dependent fluorescent

by using variable speed drives with feedback control. For example, cool air demand could

lighting is a large proportion of your site load, you may want to consider replacing the existing

be matched to the air temperature in a

lighting equipment with modern high-frequency

cumulative benefits of both projects will therefore be less than the sum of the two

of your all options with regard to replacement of voltage dependent loads should be carried out before you decide if voltage management is the most effective solution for your organisation.

energy savings5.

other energy efficiency measures such as

be some overlap of potential savings. The

Therefore a full and thorough financial appraisal

leading to a reduced motor load and significant

energy savings, especially when coupled with

already been installed, it is likely that there will

whole site is considered.

is low the motor speed can be decreased,

type of project could deliver proportionally larger

If you are undertaking energy efficiency projects on a site where voltage management has

realise the same overall savings when the

building. When the requirement for cool air

lighting, which is voltage independent 4. This

daylight dimming and occupancy detection.

For variable torque loads, principally pumps

management. However, this option may not

•

For fixed torque loads, such as conveyors, inefficient operation can often be eliminated by stopping the drive when it is not required. For example, installing detectors to stop a baggage handling system drive running when it is not needed can reduce the operating hours of the motors and reduce energy use.

individual projects, and it is worth making sure the likely savings are clear before making any investment decisions. HELP

3 4

Under EC Regulati on No. 245/2009 and implement ing Directi ve 2005/32/EC. The least efficient ball asts are phased out in 2010 (C and D types) and all magnetic t ypes by 201 2017 7. The same principle would apply to some other voltage dependent loads such as incandescent lamps which can often be effectively replaced with higher efficacy and lower energy LED solutions.

5

Power demand is a function of speed cubed and a 10% reduction in speed will result in a x% reduction in power demand.

 

Voltage management 13

Evaluating the potential for voltage management MENU

To find out whether you can save energy from voltage management, a site survey should be carried out and the potential energy savings calculated. A suitably qualified electrical engineer should be appointed to carry out any measurements and load assessment on electrical infrastructure.

Steps for the survey are:

•

D: Identify any critical loads

•

A: Measure voltage and power

•

E: Calculate potential energy savings

•

B: Measure voltage drops across the site

•

F: Decide power rating of voltage

•

C: Determine the proportion of energy

management equipment.

consumption that is voltage dependent

Figure 3: Site survey steps 

A: Measure voltage and power

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B: Measure voltage drops across the site

C: Determine the proportion of energy consumption that is voltage dependent

D: Identify any critical loads

E: Calculate potential energy savings

F: Decide power rating of voltage management equipment.

 

Voltage management 14

Figure 4: Technical considerations 

A: Measure voltage and power

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What should you measure?

What is the voltage drop and why is it important?

The voltage level at the incoming supply point(s) of a site should be logged to determine the maximum and minimum voltages, showing how voltage varies over time and with changing power demand.

Between the incoming supply point and electrical equipment supplied within a site there will be a reduction in voltage. This is due to the size and l ength of electrical cabling and the amount of power being transmitted. This ‘voltage drop’

The voltage and current for all phases should be logged and the total power calculated to give an indication of how supply voltage and power demand interact.

should be no more than that r ecommended in the Wiring Regulations.

The data from the logger should be used to calculate the lowest operating voltage on the site to determine a suitable reduction in voltage.

If you’re considering voltage management it’s important to make sure that the electricity supply to all electrical devices is always within their stated operating conditions. To ensure that this is the case, you need to know the maximum voltage drop that occurs across the site.

When and how long should you measure it for?

When and how should voltage drop be measured?

Logging should be carried out for a minimum period of seven days and recorded as averaged at five or ten minute

Voltage drop only occurs when power is being transmitted. It is therefore essential that the circuits being measured are loaded – in other words you should t ake measurements when the site is in normal use.

intervals. This should be performed when the operation of the site is expected to be typical rather than at a time of low electricity demand. Longer duration logging may be required for sites with different operational profiles. Loggers of this type need to be installed by qualified personnel.

Why is the minimum and maximum voltage important? important? The resultant data will allow the minimum and maximum voltages to be determined. This This will allow the potential percentage voltage reduction to be identified and determine whether fixed or variable ratio equipment is most suitable. HELP

B: Measure voltage drops across the site

6 Many

Voltage drop is measured by simultaneously logging the voltage at the incoming supply, and taking comparison measurements of voltage at various points around the site. The maximum voltage drop should be calculated as a percentage of the incoming voltage. You may notice particularly high voltage drops in outlying circuits such as car park l ighting. T These hese may limit the maximum voltage reduction that can be made without

C: Determine the proportion of energy consumption that is voltage dependent

What proportion of the energy consumption is voltage dependent? To determine how much energy you are likely to save through voltage management, you’ll need to assess how much of your energy use voltage dependent equipment is responsible for.

How do you determine what is voltage dependent versus voltage independent? As a starting point, it ’s useful to establish your site’s average electricity demand profile. You You can do this by looking at the profile obtained fr om the voltage logger 6 and comparing it with any half hour data  you have to ensure that the logger profile is representative of site demand. You’ll also need to check that the adopted profile takes issues such as seasonal variations into account. The next step is to carry out a walk round survey to identify the type of loads present at a site; whether they are voltage dependent or independent, their size and operating hours. From this information you will be able to develop a ‘bottom-up’ load profile, banded by voltage dependent and voltage independent loads that you can compare with the average actual profile previously determined. The more accurately the profile emerging from the walk round survey matches the actual load profile, the more accurate your savings estimate will be.

alterations e.g. changing the cabling arrangements to the car park.

sites have half-hourly electricity meters and electricity suppliers are obliged to provide customers with the resulting half hourly data. It is very useful to compare a full 12-mon 12-month th data set

with that resulting from the power logger, you can check the annual maximum demand in kVA, which may occur at a particular time of year to ensure that any equipment you buy will be adequately rated to supply this demand and you can check for average demand in KW for use in the savings calculations.  

Voltage management 15

D: Identify any critical loads

E: Calculate potential energy savings

F: Decide power rating of voltage management equipment

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Why is it important to identify critical loads?

How is this done?

Why is sizing of equipment important?

It is important to identify any safety or business critical electrical equipment such as IT infrastructure, process or medical equipment, or imported equipment that could be adversely affected by a reduction in voltage. Before making any changes you’ll need to check check that business critical electrical equipment will remain within the operating conditions specified by its manufacturer. manufacturer.

You can calculate your potential energy savings from the potential voltage reduction, whether this is for a fixed or variable ratio VM device or a r eplacement transformer. and the proportion of the annual energy consumption that is voltage dependent.

Undersized equipment will run hot and eventually fail, possibly with significant consequences, while oversized equipment will introduce unnecessary losses and could be needlessly expensive. It is important to use the 12 months of half-hourly data to get the correct size of unit that will supply the site’s maximum demand (kVA). Don’t forget to also factor in any known growth plans for the site.

For a fixed ratio voltage management device, the percentage energy saving will be the product of the annual energy consumption, the percentage by which the voltage can be reduced and the percentage energy saving per percentage voltage reduction. An example calculation showing the points to consider is given in the next section. For a variable ratio voltage management device, the percentage energy saving is calculated differently to take into account the variation in percentage voltage reduction which is linked to variations in supply voltage. For a replacement transformer the savings from reduced losses can be calculated as described on page 10. Savings from voltage reduction can be calculated as for a fixed ratio voltage management device.

Safety notice THE CONNECTION OF VOLTAGE LOGGING EQUIPMENT AND MEASURING VOLT DROPS ACROSS THE SITE IS A POTENTIALLY HAZA RDOUS TASK. IT SHOULD BE CARRIED OUT BY APPROPRIATEL APPROPRIATELY Y QUALIFIED STAFF STAFF,, ONCE A FULL RISK ASSESSMENT HAS BEEN COMPLETED, AND IN ACCORDANCE WITH AN AGREED METHOD STATEMENT STATEMENT THAT ADDRESSES THE RISKS. HELP

 

Voltage management 16

Calculating the energy savings MENU

The energy savings that result from voltage

To illustrate the calculation methodology we

1. Power demand and

management are the product of:

will use a simplified, fictitio fictitious us case study: Anywhere Admin Centre. The majority of the

operating hours

1. The power demand and operating hours 2. The percentage voltage reduction 3. The percentage power reduction per percentage of voltage reduction

employees at the site work five days a week, but a number of critical departments and the powerful IT equipment operates 24/7. There are three principal types of loads on the site:

1. Mains voltage halogen lighting in the sales and communal areas – 20kW. 2. Older type fluorescent lighting in the office space – 50kW

3. ICT equipment – 30kW. Maximum load on the system is 100kW.

The first task is to look at the average weekly power profile and decide how many operating periods to divide each week into. Our case study presents a simple example with constant daytime and evening/weekend loads so two time bands are adequate – weekdays and evenings/weekends. In more complex operations you may need to break the day up into several time slots to get an accurate model. In our example, if the public areas of our building operate on a Saturday but most of the offices are closed then we would need to add an additional time band for Saturday daytime. For each of these time periods it is important that you reconcile the measured maximum demand with the combined demand derived

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from the walkabout survey of the equipment

 

Voltage management 17

operating at that time. Ideally these approaches

2. Percentage voltage reduction

should balance. If in our case study the logger indicated that the evening’s load was, for example, 50kW, it would indicate that either we had underestimated the loads (more offices were lit overnight than we had thought) or missed something (10kW of car park lighting

To calculate the possible voltage reduction you will need to know: •

your target minimum supply voltage

•

the lowest normal supply voltage at the point of supply

had been overlooked). MENU

•

the maximum volt drop across the site.

From this information you can calculate the percentage voltage reduction you can apply.

Step 1: Power demand and operating hours survey is tabulated in time bands as set out below. Weekday day time (40hrs)

Evenings & weekend (128hrs)

load kW

load kW

20

0

3. Percentage power reduction per percentage voltage reduction The power demand of a simple resistive load is: 2 

Power =

Voltage  Resistance 

This means that for a simple resistive load a Office lights (inductive ballast fluorescent) ICT equipment

50

30

10

HELP

the Anywhere Admin Centre has decided that he would like all equipment to have a minimum supply voltage of 225V. The supply voltage changes with the time of day. At night it can get as high as 250V while during the day a minimum voltage of 245V can be seen. The greatest

normal working day this can be 5V less than the point of supply. The current lowest site voltage is 240V(245v 240V(2 45v less 5V), while the desired minimum voltage is 225V – so we have the potential to reduce the voltage by 15V or six per cent.

deliver a two per cent reduction in power and

voltage dependent. To calculate the impact of,

energy demand.

say, a voltage reduction, we need to calculate

30

40

top floor of the building. During the

one per cent reduction in supply voltage will

Most sites will have a mixture of different types

100

The facilities engineer responsible for

voltage drop occurs on supplies to the

The information from the walkabout

Reception lights (mains voltage halogen)

Step 2: Percentage voltage drop

of equipment which are either voltage dependent, voltage independent or partially

for each time period an aggregate power reduction for each percentage reduction in the supply voltage.

 

Voltage management 18

Step 3: Percentage power

The total figure for the site during the normal working day is 1.3 per c ent reduction in

reduction per percentage voltage reduction  

power demand for a one per cent reduc tion in supply voltage.

The mains halogen lights are voltage dependent and the power demand of these lights will be reduced by two per cent for MENU

Load

Demand kW

Proportion of load %

% site power reduction per % voltage reduction

Voltage dependant

100

2

20

20

0.4

each one per cent of voltage reduc tion. These lights amount to 20 per c ent of the

Fluorescents (inductive ballast

90 7

1.8

50

50

0.9

daytime load which will be reduced by (2 x 20 per cent) = 0.4 per c ent per one

Partially voltage dependant

ICT equipment

Voltage independent

0

0

30

30

0.0

equipment is wholly voltage independent and will contribute no reduction. Fluorescent (inductive ballast) lighting is partially voltage dependent (at least 90 per cent) and therefore we will get 90 per cent x two per cent = 1.8 per cent power reduction per one per cent voltage reduction. This load is 50 per cent of the overall site demand and contributes a

10 0

cent reduction in on site power demand as a result of a one per cent reduction in supply voltage.

1.3

At evenings and weekends the calculation is as follows: Load

% dependency

% impact of 1% volt reduction

Demand kW

Proportion of load %

% site power reduction per % voltage reduction

Halogen lights (mains voltage)

Voltage dependant

100

2

0

20

0

Fluorescents (inductive ballast

Partially voltage dependant

90 8

1.8

10

50

0.45

ICT equipment

Voltage independent

0

0

30

30

0.0

further 1.8 per cent x 50 per cent = 0.9 per

7

% impact of 1% volt reduction

Halogen lights (mains voltage)

per cent voltage reduction. The ICT

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% dependency

40

0.4 5

8

Clients may wish to contact OEMs to determine the exact power demand for change in voltage input. Clients may wish to contact OEMs to determine the exact power demand for change in voltage input.

 

Voltage management 19

4. Calculating the energy and cost savings Using the information you now have you can calculate the projected energy savings which are the product of:

MENU

Part 4: Calculate the savings

The weekly energy savings of 450 kWh

 

represent a 4.9 per cent saving.

Applying the values already determined,

The site operates 52 weeks p er year and

we get the following energy savings for

pays 10p per KWh supplied, giving an

our two time periods:

annual cost saving of £2,340.

•

The power demand.

•

The operating hours.

Load

•

The percentage voltage reduction.

Load KW

•

The percentage power reduction per

Operating hours

percentage of voltage reduction. For each time period you need to multiply

Daytime (40 hrs/week)

100

40

40

128

4,000

5,120

% voltage reduction

6%

6%

% site power reduction per % voltage reduction

1.3

0.45

Weekly energy saving kWh

312

138

Weekly energy consumption kWh

the load (kW) by the length of the time period (hrs) by the percentage voltage reduction and the percentage power reduction per percentage of voltage

Evening & weekends (128 hrs week)

reduction (Remember this is a ratio not a percentage and the number you use will be in the range 0-2). Finally you’ll need to consider other potential impacts.

HELP

supply voltage. You’ll need to check that lighting

The losses introduced by the voltage

levels will not fall below recommended design

management device should also be taken into

levels as a result of reducing the supply voltage.

account. Whilst typically very low, especially for

Some voltage management devices offer small

larger units, these losses will lessen the savings to a certain degree.

Lighting equipment is designed to produce

additional energy savings benefits through their

rated light output at the nominal supply

ability to improve the power quality. These

Once you have assessed how much you

voltage (in this case 230V). The light output will be reduced as a result of reducing the

potential benefits are specific to the quality of power on individual sites, so they’ll need to be

could save through voltage management, you can compare the benefits to those of

assessed and verified verified on a case- by-case basis.

alternative energy efficiency projects.

 

Voltage management 20

MENU

Practical considerations

Annual maintenance

Guaranteed savings

You will now have been able to assess the energy saving benefits of voltage management

Does the equipment need to be regularly maintained, and if so has this been factored into

These offer assurances that the predicted saving will materialise against a given baseline. Saving

specific to your site. Before installing equipment

the payback calculations? Voltage management

guarantees should be supported by a baseline

there are a number of practical considerations to

equipment typically does not require

that has been determined through monitoring

be taken into account:

maintenance, although it may be sensible to

and supported by half-hourly metering. These

regularly check that it is set up to provide the

should be agreed by both the client and the

optimum voltage, as the incoming supply could

equipment provider, and backed up by a

have changed.

statement outlining the methodology used by

Installation issues You’ll need to consider how much space new equipment will need, the best location for it, as well as taking into account the cabling and

By-pass switch

both parties to resolve any disputes.

Efficiency of voltage management equipment

controls. Do you have a safe location for it,

Do you want to install a by-pass switch to take

where it is adequately ventilated and there will

the equipment off-line for replacement or

not be any heat build-up or noise issues?

maintenance? It may make future changes

Different options may have differing levels of

easier.

efficiency. Some equipment needs additional

Transformer replacement

auxiliary equipment to maintain operation. You’ll

Fixed ratio or variable ratio? No additional space is required for this option as it is a direct replacement. An additional benefit is

Both options have their advantages, the

a new transformer with a projected 30-year life.

fixed ratio device drops the voltage level by

also need to think about the efficiency of the voltage management equipment to maximise the benefits.

a set percentage regardless of incoming voltage and is less technical technically ly complex.

Variable ratio devices provide a fixed output voltage by varying the percentage drop dependent on incoming voltage. This can minimise the risks of under-voltage and also improve the utilisation of a device. HELP

Safety first Work on electrical systems should be left to a suitably qualified person.

 

Voltage management 21

Glossary MENU

DNO Distribution Network Operator – the organisation responsible for the local electricity supply cables and infrastructure.

Phase balancing Commercial and industrial premises are provided with a three-phase electricity supply, which is necessary for many electric motors. Most electrical equipment requires just a single phase supply. Where single

a poor power factor. There is often a good payback to be had by fitting PFC to improve the power factor at a site. Power factor penalties are only an issue for larger consumers, so you should check with your supplier if you are charged a penalty for this. For

Harmonics Some electrical equipment, such as variable speed drives and regulated power supplies, can impose electrical interference or ‘harmonics’ on the electricity supply. This can cause interference with other equipment and cause slightly increased losses within transformers other electromagnetic electromagnetic equipment. Site operators are obliged to keep harmonics within specified limits.

phase is installed on a site a threephase equipment supply, it needs to be shared or with ‘balanced’ across the three phases. If this is not the case the imbalance can, in the extreme, cause three-phase equipment, such as motors, to operate inefficiently or incorrectly.

more information on PFC, refer to Carbon Trust Technology Guide CTG007.

HV High voltage – an alternating current supply voltage in excess of 1000V. In the UK the majority of sites with a HV supply voltage will be supplied at voltage of 11,000V (11kV). LV Low voltage – an alternating current supply voltage less than 1000V. An LV supply in the UK from the DNO is currently 400V three phase or 23 0V single phase +10% -6%. Moving to ±10% in 2011/12.

Power factor The ratio of useful power to total power as drawn from an AC supply by an electrical device or installation. In most instances a poor p ower factor is caused by the magnetising power required by equipment such as electric motors. The c ables within electricity supply networks and on sites need to deliver the total p ower (useful and magnetising power). Poor power factor can reduce the capacity of cables, etc, to deliver useful power. Power Factor Correction (PFC) Since poor power factor reduces the capacity of a DNO’s network to deliver useful power, most electricity tariffs are structured to penalise sites with

Impedance A measure of the opposition to the flow of an alternating current in a circuit; the aggregation of its resistance, inductive and capacitive react ance. Inductance A measure of the inertial property of an electrical device caused by the magnetic field created that opposes the flow of an alternating current through the device. Transient voltages Transientt voltages are ver y short duration spikes Transien caused by switching and faults on the electricity network. In extreme cases these can cause catastrophic damage to equipment. Smaller transients can shorten the life expectancy of electrical equipment.

HELP

 

The Carbon Trust is a not-for-profit company with the mission to accelerate the move to a low carbon economy. We provide specialist support to business and the public sector to help cut carbon emissions, save energy and commercialise low carbon technologies. By stimulating low carbon action we contribute to key UK g oals of lower carbon emissions, the development of low carbon businesses, increased energy securit y and associated jobs.

We help to cut carbon e missions now by: •

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•

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We reduce potential future carbon emissions by: •

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•

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www.carbontrust.co.uk 0800 085 2005

The Carbon Trust receives funding from Government including the Department of Energy and Climate Change, the Department for Transport, the Scottish Government, the Welsh Assembly Government and Invest Northern Ireland. Whilst reasonable steps have been taken to ensure that the information contained within this publication is correct, the authors, the Carbon Trust, its agents, contractors and sub-contractors give no warranty and make no representation as to its accuracy and accept no liability for any errors or omissions. Any trademarks, service marks or logos used in this publication, and copyright in it, are the property of the Carbon Trust. Nothing in this publication shall be construed as granting any licence or right to use or reproduce any of the trademarks, service marks, logos, copyright or any proprietary information n any way without the Carbon Trust’s prior written permission. The Carbon Trust enforces infringements of its intellectual property rights to the full extent permitted by law. Any trademarks, servicemarks or logos used in this publication are the property of the Carbon Trust and copyright is licensed to the Carbon Trust. Nothing in this publication shall be construed as granting any licence or right to use or reproduce any of the trademarks, service marks, logos, copyright or any proprietary information in any way without the Carbon Trust’s prior written permission. The Carbon Trust enforces infringements of its intellectual property rights to the full extent permitted by law. The Carbon Trust is a company limited by guarantee and registered in England and Wales under Company number 4190230 with its Registered Office at: 6th Floor, 5 New Street Square, London EC4A 3BF. Published in the U K: June 2011. © The Carbon Trust (June 2011). All rights reserved.

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