Most industrial and commercial facilities consume sizable amounts of electricity to fulfill their goals. These facilities are often equipped with a standby generator that is called into operation during an interruption of the incoming utility supply.
However, when these facilities are equipped with a cogeneration system, specialized design and system protection aspects must be considered.
What is a Cogeneration System?
Cogeneration system is configured to work in parallel with the utility system to curtail the net power consumption
A cogeneration system is different than a traditional standby generator. A cogeneration system is configured to operate in parallel with the utility system to curtail the net power consumption from the utility supply.
By properly configuring a cogeneration system during its initial design, they can reduce the electricity bill and have their cogeneration system act as a standby source of power in the event of an electrical utility outage.
How Does a Cogeneration System Work?
A cogeneration system is usually associated with an industrial process. When utility power is available, the cogeneration system will electrically synchronize against the utility source to operate in tandem to reduce the electrical consumption (known as the “Base Load” mode of operation).
During a utility outage, the cogeneration system will operate in a standalone configuration to provide backup power to the facility (known as the “Isochronous” mode of operation).
Importance of Anti-Islanding Protection
Islanding occurs when a cogeneration system continues to back-feed the utility grid when the normal supply from the electrical utility company is interrupted. It is important to avoid an islanding condition because the reverse power flow into the utility grid from the cogeneration system can pose major safety hazards to the utility company line workers who may not realize that a circuit is still powered.
Islanding can also result in costly damage to the cogeneration system equipment due to unregulated voltage and frequency conditions.
How to Establish Effective Anti-Islanding Protection?
If they can sense an “islanding” condition, they can effectively isolate a cogeneration system to prevent injury to personnel and damage to the electrical equipment. They can use both relaying and control methods to sense an islanding condition to effectively isolate a cogeneration system.
- Relaying Method: They can isolate a cogeneration system within two (2) seconds or less by using a combination of ANSI-81U (under frequency) protection in conjunction with ANSI-32 (reverse power), ANSI-67 (directional overcurrent), and ANSI-50BF (stuck breaker) protection.
- Control Method: By using a transfer-trip philosophy, they can create an automated control scheme via communication between the utility company’s power substation and the on-site cogeneration facility. More modern methods allow the utility company to issue a high-speed signal via GOOSE Messaging (IEC 61850) or Mirrored Bits. This scheme can be accomplished via fiber-optic communication, wireless communication, or a carrier frequency signal tuned into the utility company’s power distribution lines.
