Archive for the ‘G59’ Category

Short Term Infrequent Paralleling Issues

Friday, April 9th, 2010

Short term infrequent paralleling is usually applied to standby power supplies that are designed to support a customer’s islanded network and literature review for dissertation allows for seamless transfer following restoration of supply or for load transfer during routine testing.

Acceptable number of, and duration of paralleling time.
G59/1 allows for the infrequent connection of generation with, (at the DNO’S discretion,) a relaxation in protection requirements. No hard and fast definitions are given for “infrequent” but a figure of once per month is suggested. The number of parallel operations should be at the discretion of the individual DNO based on the capability of the network. However if it is required to test more than once a week then this would no longer be considered as infrequent paralleling.

Once operating in parallel, the generator is allowed to remain in parallel for a maximum of 5 minutes. The duration of the parallel should be kept as short as is reasonably practical for change over to take place. Less than 1 minute is normally achievable with longer times only being required if the equipment is incapable of shorter change over. After this time the parallel has to be broken automatically by a timer. This timer should be a separate device from the changeover control system such that failure of the auto changeover system will not prevent the parallel being broken.

Summary: In order for the generator to be considered as operating as “short term infrequent paralleling”, it must not be allowed to connect in parallel for more than 5 minutes in any month, or more frequently than once per week. If the duration of parallel connection exceeds this period, or this frequency, then the generator must be considered as if it is, or can be, permanently connected.

Protection Requirements

Short term occasional parallel operation requires only basic under /over voltage and under /over frequency protection.

A timer separate from the normal changeover control system should be provided to break the parallel if the normal means of changeover should fail.

This protection only needs to be in operation for the time the generator is operating in parallel.

Loss of mains protection in the form of ROCOF and Vector shift are not required, although many G59 multifunction relays now have this function built in as standard.

Similarly additional requirements such as NVD, intertripping and reverse power are not required.

This is based on the assumption that during the year the generator is only likely to be in parallel for a maximum of 1/8760th of the time and therefore the chance of a genuine loss of mains event coinciding with the parallel is unlikely.

If a coincidence did occur, the possibility of the generation supporting the Island also becomes a factor. Under voltage / under frequency is likely to trip the generation off if the load is greater than the generation capacity. Consideration could be given here to applying different settings for short term parallel connection. As this generation will not be expected to give grid Support or contribute to P2/6 security, more sensitive settings e.g. 49.5 Hz -6%V would compensate for lack of LOM protection?

Ultimately if an island was established the situation would only persist for the duration of the parallel operation timer setting before generation was tripped.(Auto Reclose excepted)

Generator Star point Earthing
For HV connected generation ETR113 Fig 5.6 shows that for short term parallel the star point of the generator should remain connected to earth.
It is recommended that for LV generation operating in short term parallel the same should apply for the following reasons.

• Having switches in the generator earthing circuits, that for the majority of the time will need to remain closed creates an unnecessary complication / risk of failure of leaving an unearthed system.

• Multiple earths on the system could result in circulating third harmonic current around the neutral earth path. This could result in heating of the cables, however as this is a thermal rating issue with a relatively long time constant the short period of parallel operation is unlikely to result in any serious overheating.

Very Short Term Parallel

Some manufacturers are now installing their standby machines with Fast acting Automatic Transfer Switches. These are devices that only make a parallel connection for a very short period of time, typically 100 – 200mS. Under these conditions installing a conventional G59 relay with an operating time of 500mS is not appropriate when the parallel will normally be broken before it has a chance to operate. There is however the risk that the device will fail to operate correctly. Therefore a backup timer should be installed to operate a conventional CB if the parallel remains on for more than 1 Sec.

Contribution to fault level
For short term infrequent parallel there is the need to consider the effect of the generation contribution to fault level. If any problems are identified, then the process for controlling this risk will need to be agreed with the Network Operator.

Voltage Rise / Step Change
Networks should be designed such that the connection of a generator under normal operating conditions does not produce voltage rise in excess of the statutory limits. In general this should not be an issue with most short term parallel operation as at the time of synchronising with the mains most sites will normally be generating only sufficient output to match the site load. Therefore the power transfer on synchronising should be small, with the generator ramping down to transfer site load to the mains. If the generator tripped at this point it could introduce a larger voltage step change than would normally be acceptable for loss of a long term parallel generator but in this event it could be regarded as an infrequent event and a step change of up to 10% would be acceptable*
(* assuming this is the figure the DNO agree to).

Breaker out of phase switching capability
For a new metering point the metering circuit breakers should have an out of phase switching capability.

For an existing installation that does not require replacement of the metering breaker for any other reason, then for short term parallel the risks of out of phase opening are low. Therefore replacement of the metering circuit breaker should not be necessary. It is assumed however that the generator synchronising breaker would have out of phase capability.

TECHNICAL – Electrical Supply Standards and Other Documents

Wednesday, May 20th, 2009

Standards and Other Documents

Electricity Safety, Quality and Continuity Regulations (ESQCR)
The Electricity Safety, Quality and Continuity Regulations 2002 – Statutory Instrument Number 2665 -HMSO ISBN 0-11-042920-6 abbreviated to ESQCR in this document.
[Available FoC on DTI web site:]

BS EN 50160 Voltage characteristics of electricity supplied by public distribution systems

BS 7671: 2001 Requirements for Electrical Installations IEE Wiring Regulations 17th Edition.

Distribution Codes
a) The Distribution Code of the DNOs of Great Britain

[Available FoC on Distribution Code website]

b) The Distribution Code for Northern Ireland

Grid Codes

a) The Grid Code for England and Wales
b) The Grid Code for Scotland
c) The Grid Code for Northern Ireland

Engineering Recommendation G5/4-1 (2001)
Planning levels for harmonic voltage distortion and the connection of nonlinear equipment to transmission and distribution networks in the United Kingdom.

Engineering Recommendation G12/3

Requirements for the application of protective multiple earthing to low voltage

Engineering Recommendation G59/1, Amendment 1 (1995)
Recommendations for the Connection of Embedded Generating Plant to the Regional Electricity Companies’ Distribution Systems.

Engineering Recommendation G74
Procedures to meet the requirements of IEC 909 for the calculation of short circuit currents in three phase AC power systems.

Engineering Recommendation G75/1, (2002)
Recommendations for the connection embedded generation plant to public distribution networks above 20kV or with outputs over 5MW.

Engineering Recommendation G83/1-1 (2003)
Recommendations for the connection of small-scale embedded generators (up to 16A per phase) in parallel with public low-voltage distribution networks.

Engineering Recommendation P2/6
Security of Supply

Distribution planning standards of voltage and of security of supply. (Parts of
Scottish Hydro Electric Power Distribution Ltd Area)

Engineering Recommendation P14
Preferred switchgear ratings.

Engineering Recommendation P24
AC traction supplies to British Rail.

Engineering Recommendation P25
The short circuit characteristics of electricity boards low voltage distribution
networks and the co-ordination of overcurrent protective devices on 230V single phase supplies up to 100A.

Engineering Recommendation P26/1
The estimation of the maximum prospective short circuit current for three phase 415V supplies.Engineering Recommendation P28 (1989)
Planning limits for voltage fluctuations caused by industrial, commercial and domestic equipment in the United Kingdom.

Engineering Recommendation P29 (1990)
Planning limits for voltage unbalance in the UK for 132 kV and below.

Electricity Association Engineering Recommendation S34 (1986)
A guide for assessing the rise of earth potential at substation sites, 1986.

Electricity Association Technical Specification (EA TS) 41-24 November 2009
Guidelines for the design, installation, testing and maintenance of main earthing systems in substations,.

Engineering Technical Report No. 113, Revision 1 (1995)
Notes of Guidance for the Protection of Embedded Generating Plant up to 5 MW for Operation in Parallel with Public Electricity Suppliers’ distribution systems.

All Engineering Recommendations are available from:

Energy Networks Association
18 Stanhope Place
Marble Arch
W2 2HH
Tel: 0207 706 5100
Fax: 0207 706 5101

Electrical Grid Connected Generation & DNO’s

Wednesday, May 20th, 2009

Grid Connected Generation

Terminology to Start

• Developer

– You!

• Distribution Network Owner/Operator (DNO)

– Owns, maintains, develops and operates the physical network
– SP Manweb, United Utilities in the North West
– Not the slightest bit interested in selling or buying energy from you

• Electricity Supplier

– Party to contract with to buy & sell energy
– Npower, PowerGen, Scottish Power, British Gas, etc…
– Not the slightest bit interested in the physical connection

• Ofgem

– Electricity and Gas Market regulator
– Also administers the ROC process if your technology is eligible

Just Some of the Legal Issues

• If grid connected, then it is a legal requirement to have permission to connect & operate any form of generation

– Needs to have a DNO connection agreement
– Needs to have correct electrical protection
– Needs to have correct earthing
– Needs to have an export meter (if exporting)
– Needs to have a supplier contract (if exporting)

• D-code : Distribution Code for UK Distribution Networks

• G-code : Grid Code for UK Transmission Networks

• Electricity at Work Regulations

Engineering Recommendations

• Technical connection requirements are detailed in the Engineering Recommendations

– DNOs view these as “Rules” rather than just “Recommendations”

• G83: Less than 6kW (16A/phase)

– No connection agreement required but must notify DNO once on

• G59: Less than 5MW and less than 20kV connection

– Must have a connection agreement

• G75: Anything else up to 50MW or transmission connected

– Must have a connection agreement

DNO Responsibilities

• Statutory obligations under the terms of their licence

– Secure operation and development of the network
– Safe & reliable operation of the network
– Ensure fair and equal access to the network
– Least cost options for connection
– Lifetime of network not just your connection

• Must respond to a connection application within 90 days. Remember, they’re not out to get you, but they have responsibilities too!

 Electrical Connection Issues

• Technical issues to be considered during connection study/investigation

– Thermal limits
– Voltage limits & step change
– Reverse power-flows through transformers
– Short-circuit rating of switchgear
– Protection arrangements & co-ordination
– Harmonics & Power Quality
– Transient stability (usually only for larger generators)

• Energy Metering

• There will be the need to provide a reasonable level of data on the generator and the site connections

• The connection and protection will need to be witnessed and approved by the DNO in order to complete the connection process

 Network Capacity Issues

• The Distribution Network has real limits

• Due to load growth and the drive towards maximising use of existing assets, available headroom is often quite limited

– Cable ratings reached during peak load
– Voltage drop/rise reached
– Circuit breaker short-circuit limits reached

• The Capacity Race

– It is not just fiction it is unfortunately real in some locations
– First-come, first-served & Interactive Applications
– There are some solutions but most do add cost and complexity

 Rule of Thumb Connection Capacities

< 6kW 240V
< 1MW 415V (3-phase)
< 1-10MW 11kV
< 30MW 33kV
< 50MW 66kV/132kV
> 50MW 132kV upwards & National Grid interfaces…

As with any project, the bigger the project, it is important that you have the right level of advice or expertise to de-risk the project.

 So, what do I do to get connected?

• Contact your friendly neighbourhood consultant ☺

But seriously:

• Start with a rough idea of what you want to do

– Check that your site can fit it and you can afford it
– Check that all other regulatory issues are okay

• Have an informal “chat” about connection possibilities with DNO generator connections or knowledgeable person

– Check that your initial idea still sounds sensible

 When contacting the DNO

• Contact DNO – generation connections (NOT Demand)

– The connection process will be more likely to be successful with good communication between the developer and the local DNO

• Determine your connection route: G83, G59 or G75
– This may have costs associated with it

• Be prepared for a process not just rubber stamping

– Planning & Information phase
– Detailed Design phase
– Installation phase
– Testing & Commissioning phase

 Working with the DNO

• Seek an early meeting to discuss your project

– Outline the scheme
– Discuss the DNO’s process for connections
– Request an indicative connection design and budgetary cost estimate with a split between contestable & non-contestable works

• Review your project

– Submit the formal connection application
– Remember to accept the connection offer!

• Submission of data to DNO

– Make sure that this is appropriate and timely to avoid delays

• Testing and Commissioning

– Plan in advance to avoid delays as staff will usually be quite busy

 Connection Charges

• Application Fees

– These vary between DNO and size and voltage level of project
– Complex projects may involve additional fees

• Connection Assets

– Developer will be expected to pay full costs for all sole-use assets

• Generation Use of System Charges

– Site dependent & in lieu of network reinforcement costs
– Each DNO has own policy in-line with Ofgem guidance

Competition in Connections

• Developer as two options:

– Get the DNO to do all works necessary for the connection
– 3rd party to provide all contestable works which DNO then adopts

• Contestable Works

– Supply & installation of any new assets up to the point of connection to the existing network. Adoption agreement required.

• Non-Contestable Works

– Any studies, reinforcement or installation on existing network
– Design & specification of any new assets, consents & way-leaves

• Note: The DNO will not get involved in any “on-site” works

 Finally, just when you thought it was too easy

Other non-electrical issues still need to be resolved

– Planning Permission?
– EIA, Emissions?
– Health & Safety?
– Commercial?
– Installation & transport?
– CDM?