# Presentation: 753051

## Interconnection Requirements & Parallel Operations of Non-Utility Generation

- David Dykes
- Southern Company
- FUPWG Spring Meeting
- 23 April 2004

## Topics

- Utility’s Objectives
- Interconnection Issues
- Power Flow
- Utility Issues
- Utility Responsibilities
- NUG Responsibilities
- Utility Interface Examples
- References

## Utility’s Objective

- To establish minimum requirements, from the Utility’s perspective, for the connection of Non Utility Generators (NUG)
- NUG will be permitted to operate in parallel with Utility system provided there is no negative impact on the safe operation of the system or the level of service to other Utility customers.

## Interconnection Issues

- The interconnection requirements are intended to achieve the following:
- Insure the safety of the general public and Utility personnel
- Minimize the possible damage to property of the general public, Utility, or Utility’s customers
- Minimize adverse operating conditions on the Utility’s system (Reliability)
- Prevent subsidization of NUG owner by other rate payers unless mutually benefited

## Interconnection Issues

- The determination of protective devices required depends primarily on three major factors:
- The type and size of the generating equipment;
- The geographic location of the NUG on the Utility system, and;
- The manner in which the installation will operate (one–way vs. two–way power flow).

## Interconnection Issues

- In addition to the protective devices, certain modifications and/or additions may be required to the Utility system. ***Each request for interconnection is unique.***
- The NUG owner shall bear that portion of the costs resulting from equipment additions or changes required to permit parallel operation of the NUG.

## Power Flow

**One-Way Power Flow** - NUG owner does not intend to sell or flow energy to Utility
**Two-Way Power Flow** - NUG exports power to Utility system. Utility system protection and control scheme design based on existing sources of energy to a faults on the system. Adding a generator creates a new fault current source which must be cleared, thus requiring significant changes to existing schemes

**Notes:**
intertie protective relaying must be installed which can sense faults while still allowing power flow in both directions

## Utility Issues

**Faults** - NUG can be a contributor of fault current to a fault on the utility system
**Reclosing** - Utilities employ automatic reclosing schemes to a dead circuit and does not employ any voltage check, phasing, or synchronization schemes
**Islanding** - If isolated system still operating when the utility source returns, damage is likely as the two systems will be out of phase.
**Cost** - All non-system beneficial costs to be borne by NUG owner

## Utility Responsibilities

**Protective Devices** - Utility shall own, operate and maintain all protective equipment associated with the inter-connection to insure functionality;
**Utility Grade Relays** - to promptly sense abnormal system conditions and initiate the isolation of the problem area
**Instrument Transformers** - relaying accuracy class devices

## Utility Responsibilities

**Protective Devices (Con’t)**
**Circuit Breakers** - Utility shall own, maintain, and operate the intertie circuit breaker at all large NUG installations
**Single–Phase Devices - Fuses/Oil Circuit Reclosers** – Replacement of to Minimize the possibility of single–phasing a NUG’s three–phase generator
**Communication Channel** - May be required in cases where necessary to remotely signal removal of NUG from Utility system due to fault or other abnormal conditions not sensed by protective devices at NUG location

## NUG Responsibilities

**Operating Limits**
**Voltage** – NUG shall maintain plus/minus 6.0% of the nominal voltage
**Flicker** – NUG shall not exceed 2% as measured at the primary side
**Frequency** – NUG shall not deviate more than one–half hertz on a 60 hertz base
**Power Factor**- NUG shall maintain between 0.85 leading to 0.85 lagging.

## NUG Responsibilities

**Harmonics** – NUG shall not introduce excessive distortion to voltage and current waveforms and be within the limits specified
**Isolation Transformer**
**Energization of Utility Equipment by NUG**
**Synchronization of Non-Utility Generation**
**Disconnect**
**Codes and Regulations**
**Metering**

**Notes:**
Harmonics - based upon IEEE 519-1992
Isolation Xmer - This transformer is usually connected in such a manner as to isolate the zero sequence circuit of the NUG from the zero sequence circuit of the GPC system
Energization - The NUG shall not energize or de–energized GPC circuit
Sync - The NUG owner is responsible for the synchronization of the NUG to the GPC system. 
Disconnect - shall provide a visible air gap between the NUG and the GPC system in order to establish the open break to satisfy safety requirements for maintenance and repair work on the GPC system
Codes - It is the responsibility of the NUG owner to comply with applicable local electrical and safety codes

## Large NUG -Typical Transmission Interconnection Two-Way Flow

- Relaying in the Utility substation may include some or all of the following:
- _Device No_.	_Function_
- 50/51	Phase Overcurrent
- 87	Transformer Differential
- 51G/51N	Ground Overcurrent
- 63	Transformer Fault Pressure
- 21	Impedance
- 121	Impedance
- 62	Timer for 121
- 59G	Zero Sequence Overvoltage
- 59/27	Overvoltage / Undervoltage
- 81	Over/Underfrequency
- Relays trip Breaker A or both A and transformer high side AIM switch depending on conditions.
- Breaker A may reclose only if utility bank is hot and NUG bus is dead.

**Notes:**
Large NUG - Greater than 3 MVA
Small NUG - not classified as large or extremely small
Extremely Small - Generation less than 100 kVA

## Large NUG -Typical Distribution Interconnection Two-Way Flow

- Relaying in the Utility substation may include some or all of the following:
- _Device No_.	_Function_
- 59/27	Overvoltage / Undervoltage
- 81	Over/Underfrequency
- 59G	Zero Sequence Overvoltage
- 50/51	Phase Overcurrent
- 50/51N	Ground Overcurrent
- Relays trip Breaker/Recloser A.
- Breaker A may reclose only if utility source is hot and NUG bus is dead

**Notes:**
Large NUG - Greater than 3 MVA
Small NUG - not classified as large or extremely small
Extremely Small - Generation less than 100 kVA

## Small NUG -Typical Transmission Interconnection Two-Way Flow

- Relaying in the Georgia Power Company substation may include some or all of the following:
- _Device No_.	_Function_
- 59G	Zero Sequence Overvoltage
- 59/27	Overvoltage / Undervoltage
- 81	Over/Underfrequency
- 46	Negative Sequence 		Overcurrent (Current 		Unbalance)
- 62	Timer for 46
- 51	Phase Overcurrent
- 51N	Ground Overcurrent
- Relays trip Breaker A.
- Breaker A may reclose only if utility source is hot and NUG bus is dead.

**Notes:**
Large NUG - Greater than 3 MVA
Small NUG - not classified as large or extremely small
Extremely Small - Generation less than 100 kVA

## Small NUG -Typical Distribution Interconnection Two-Way Flow

- Relaying in the Georgia Power Company substation may include some or all of the following:
- _Device No_.	_Function_
- 59/27	Overvoltage / Undervoltage
- 81	Over/Underfrequency
- 59G	Zero Sequence Overvoltage
- 50/51	Phase Overcurrent
- 50/51N	Ground Overcurrent
- Relays trip Breaker/Recloser A.
- Breaker/recloser A may reclose only if utility source is hot and NUG bus is dead.

**Notes:**
Large NUG - Greater than 3 MVA
Small NUG - not classified as large or extremely small
Extremely Small - Generation less than 100 kVA

## Extremely Small NUG - Typical Distribution Interconnection One- or Two-Way Power Flow

- Relaying at the interconnection may include some or all of the following:
- _Device No_.	_Function_
- 51	Phase Overcurrent
- 59/27	Overvoltage / Undervoltage
- 81	Over/Underfrequency
- Relays trip Breaker A

**Notes:**
Large NUG - Greater than 3 MVA
Small NUG - not classified as large or extremely small
Extremely Small - Generation less than 100 kVA

## References

- “National Electrical Safety Code”, ANSI C2-1993, Published by The Institute of Electrical and Electronics Engineers, Inc.
- “IEEE Standard for Relays and Relay Systems Associated with Electric Power Apparatus”, ANSI/IEEE C37.90, 1989 (R1994).
- “Guide for Protective Relaying of Utility-Consumer Interconnections”, ANSI/IEEE C37.95, 1989 (R1994).
- “IEEE Guide for Interfacing Dispersed Storage and Generation Facilities with Electric Utility Systems”, ANSI/IEEE Std. 1001, 1988.
- “IEEE Recommended Practice for Utility Interconnection of Small Wind Energy Conversion Systems”, ANSI/IEEE Std. 1021, 1988.
- “Intertie Protection of Consumer–Owned Sources of Generation, 3 MVA or Less”, IEEE Publication 88 THO224-6-PWR
- “Reliability Considerations for Integrating Non-Utility Generating Facilities with the Bulk Electric Systems”, North American Electric Reliability Council, Princeton, NJ 08540, April 1987.
**Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems **- “Buff Book”, ANSI/IEEE Std. 242-1986 (R1991).
**Recommended Practice for Emergency and Standby Power Systems for Industrial and Commercial Applications **- “Orange Book”, ANSI/IEEE Std. 446-1995.
**The National Electrical Code**, National Fire Protection Association, Quincy, MA, 02269, ANSI/NFPA-70-1996.