NERC Requirements for Generation Stations

There are number of standards where NERC (North American Electricity Reliability Corporation) dictates specific requirements for the equipment, protection, control and operation of the transmission facilities. The below NERC standards can be referred to for this specific requirement: 

·         NERC PRC 023-2 (Transmission Relay Loadability)

·         NERC FAC-008-3 (Facility Ratings)

·         NERC PRC-025-1 (Generator Relay Loadability)

Although the current industry accepted design based on transmission code -referred to as "Good Utility Practice"- would inherently meet normal NERC requirements, the Engineer shall ensure all the requirements are met since the Client (Generator) would be subject to a NERC audit for compliance after the installation and commissioning of the generation station. 

The Engineer, needs to focus on the design requirements. However, there are more operational requirements that the Generator shall be responsible for and shall be taken into account. In other words, once the Engineer's design meets NERC requirements for reliability, that is where their obligations end.

The existing facilities that do not comply with the latest NERC requirements are allowed to continue to operate. But any major retrofit project or expansion to the existing facilities shall include additional equipment / systems to comply with the new requirements.

Our engineering and design of stations in Ontario -which is based on Ontario Energy Board's Transmission System Code- generally complies with NERC requirements. Two important aspects of generation stations that are mandatory and need to be taken into account during the initial estimate and subsequent design are as follows:    

1- There shall be two battery banks for protection and control equipment. Unlike load stations one common battery bank with two chargers would not be acceptable for generation stations.

2- There shall be a circuit breaker for switching at the switching station. Unlike load stations motorized disconnect switch would not suffice.

Those are the major two features that affect the generation stations. Other NERC requirements shall be similar to those of load stations and would not have a significant impact on the project estimate and the design.

The concern here for generation stations in wind power projects is that while in some cases the generators are derated to suit project requirements, NERC PRC 023-2 and NERC PRC-025-1 require 150% setting on transmission, transformer protection, 130% of rated nameplate of the generator (not de-rated).

This shall be dealt with closely as it could mean that the station and collector system shall be so designed to carry nameplate rated load. This will have a huge impact on the equipment while it can never happen in practice.

In wind generation facilities, loadability is limited by inherent current-limit in WTG's and the cables / transformers will not be overloaded however the relays are generally set to 10%-15% above maximum load per worst case scenario identified in the power flow study and fault overcurrent protections would be based on the fault fed from the grid. If WTG's are derated and the derated MVA has been the base for the design of stepup transformers and the collector cables, then the settings have to be selected for derated equipment loadability again by the power flow study.

The NERC standard has observation to synchronizing generator plants and transmission grid loadability which have 130% generation capability. In wind power projects with Type-4 Generator / Inverters, each generator is able to run up to 105% of its nominal rating then a 130% setting is not effective. If the design is based on /contracted for the derated WTG then the system is registered / recognized to the utility for the derated MVA not nominal generator MVA. Regardless, the generation is limited by generator manufacturer’s setting to the derated MVA.

If the generation is comparable to the grid MVA at the POI (point of interconnection), then the system stability is critical and loadability is important. In most of windfarm projects the source is considered weak-infeed and has no impact on stability then the loadability is more important to the client as profitability!    

links:
http://www.nerc.com/pa/Stand/Reliability%20Standards/PRC-025-1.pdf

http://www.nerc.com/pa/Stand/Project%202010132%20Phase%202%20Relay%20Loadability%20Generati/PRC_023_3_Transmission_Relay_Loadability_2013_06_20_Draft_3_(Clean).pdf

Bare Copper Conductor in Concrete

Bare Copper Conductor in Concrete

Some professionals are reluctant to use bare copper conductor embedded in concrete. They argue that the basic nature of concrete would be a source of corrosion. However this is not a proven argument and different codes and standards have allowed the use of bare copper embedded in concrete as a ground electrode.

The following excerpts of codes can clarify this issue\;

NEC

National electrical code  Article 093, Section E.5 only rules out Aluminum conductor for direct burial in concrete for grounding purposes:

“5. Metals used for grounding, in direct contact with earth, concrete, or masonry, shall have been proven suitable for such exposure.

NOTE 1: Under present technology, aluminum has not generally been proven suitable for such use.

NOTE 2: Metals of different galvanic potentials that are electrically interconnected may require protection against galvanic corrosion.”

NEC article 094, section B.6 specifically refers to copper conductor for use as concrete encased electrode application:

“A metallic wire, rod, or structural shape, meeting Rule 93E5 and encased in concrete, that is not insulated from direct contact with earth, shall constitute an acceptable ground electrode. The concrete depth below grade shall be not less than 300 mm (1 ft), and a depth of 750 mm (2.5 ft) is recommended. Wire shall be no smaller than AWG No. 4 if copper, or 9 mm (3/8 in) diameter or AWG No. 1/0 if steel. It shall be not less than 6.1 m (20 ft) long, and shall remain entirely within the concrete except for the external connection. The conductor should be run as straight as practical.”

CSA

Canadian electrical code Section 10 item 10-700 accepts concrete encased copper conductor as a grounding electrode.

“10-700  Grounding electrodes (see Appendix B)

(3) A field-assembled grounding electrode shall consist of

(a) a bare copper conductor not less than 6 m in length, sized in accordance with Table 43 and encased within the bottom 50 mm of a concrete foundation footing in direct contact with the earth at not less than 600 mm below finished grade”

Also in item 10-806:

“(6) Notwithstanding Subrule (2), a grounding conductor No. 6 AWG or larger shall be permitted to be embedded in concrete provided that the points of emergence are located or guarded so as not to constitute exposure to mechanical damage.”

And in table 43, the size of bare copper conductor is specified for different ampacities of the service conductor:

Table 43

Minimum conductor size for concrete-encased electrodes

(See Rule 10-700.)

Ampacity of largest service conductor or equivalent for multiple conductors, A	Size of bare copper conductor, AWG
165 or less	4
166–200	3
201–260	2
261–355	0
356–475	00
Over 475	000

Metring Plan

Ontario Transmission Code requires a Metering Service Provider (MSP) to be hired by load or generator customers for metering services. MSPs are third parties certified for the design, installation, commissioning and operation of metering equipment in HV stations.

AS a first step, MSP prepares a metering single line diagram (SLD) and sends to IESO for approval. MSP also prepares a metering plan to be submitted to IESO for approval. However, MSP does not submit the metering plan directly to the IESO as it needs to come from the Metered Market Participant (MMP). The plan needs to be updated with all the information including the MECs.

Once the SLD is approved IESO will then request package 2 to be submitted which will include the EITRP (Emergency IT Restoration Plan) and the MEC documents.  The secondary cable distances between IT's and the metering cabinet is required in order to complete the MEC calculations.