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Technical Requirements
Technical Requirements » Central Hudson » Distributed Generation » Technical Requirements

Click here for Central Hudson's Electrical Specifications and Requirements

Generators up to 5MW in size

Distributed Generation Equipment

Energy sources, such as photovoltaic and wind generation systems, are potentially dangerous if not installed with the proper safeguards. For this reason, utilities, including Central Hudson Gas & Electric Corporation, require that energy sources operating in parallel with their electrical systems include automatic disconnection functions which ensure that the customer's generation source is not electrically interconnected with the utility in the event of a system disturbance.

To ensure that these interconnections meet safety requirements, the New York State Standardized Interconnection Requirements state that interconnection applications must include documentation of proposed equipment certification, “stating compliance with UL 1741 by an NRTL (Nationally Recognized Testing Laboratory)”. In an effort to streamline the review and acceptance process, a procedure was developed in New York State that allows manufactures to have their equipment tested and certified by an independent testing laboratory. The test results are reviewed by the New York State Department of Public Service (NYS DPS). Following this review, if the NYS DPS believes that the equipment meets the necessary requirements, the equipment is categorized as Type Tested and Approved Equipment. A listing of currently approved equipment can be found on this page of the NYS DPS web site.

Transformers and Effective Grounding

When operating, all customer generation must be an effectively grounded source to the Central Hudson System. When not operating, the customer’s equipment must not be a ground source to the Central Hudson System. CHG&E Interconnection Protection Requirements document (pgs. 12-13) explains the rationale for this requirement.

A grounded wye - grounded wye transformer satisfies the requirement of being an effectively grounded source. There are other ways to be effectively grounded (see Methods of Effectively Grounding). A three-leg core type grounded wye – grounded wye transformer cannot be used; a four-leg or five-leg core type transformer or three single-phase transformers are required to prevent the regeneration of a lost phase and overheating due to zero sequence current circulating through the transformer tank.

Two main concerns when connecting to the utility through a grounded wye - delta transformer are overvoltage and backfeed. An overvoltage condition can occur if the utility protective device opens for a utility ground fault before the generator is disconnected from the utility system. The utility circuit will remain energized through the delta connection for a short period of time under this scenario. During this time, the neutral may shift to ground potential, which could result in overvoltages on the unfaulted phases of the Central Hudson system that approach phase to phase level. These overvoltages may cause damage to Central Hudson and/or customer equipment. Overvoltages are also a concern when a transformer with an ungrounded wye connection on the generator side is used for interconnection.

A transformer that is delta connected on the utility side can backfeed the Central Hudson system during an open-phase condition. An open phase on the utility side may cause a voltage (up to 50% of nominal) to remain present on the open phase. This impressed voltage presents a safety concern for our workers as well as a power quality concern for other customers connected to that phase.

A transformer that is delta-connected on the utility side or ungrounded wye connected on the generator side does not provide effective grounding on its own; a separate grounding transformer is required (see Methods of Effectively Grounding – Figure #1). The grounding transformer must be disconnected either at the high side or its neutral when the system is not generating to prevent it from being a ground source to the utility system. To be considered effectively grounded, the ratio of zero sequence impedance to positive sequence impedance must be less than three (3). Additional protection may also be required based on the results of the interconnection review.

Disconnect Switch

As required by the New York State Standardized Interconnection Requirements (NYSSIR), generating equipment with system size larger than 25 kW and non-inverter based systems of 25 kW or less shall be capable of being isolated from the utility system by means of an external, manual, visible, gang-operated, load break disconnecting switch. The disconnect switch shall be installed, owned, and maintained by the customer- generator, and located between the generating equipment and its interconnection point with the utility system.

The disconnect switch must be rated for the voltage and current requirements of the installation and switch shall be clearly marked, "Generator Disconnect Switch," with permanent 3/8 inch or larger letters.

The customer-generator will propose, and the utility will approve, the location of the disconnect switch. The location and nature of the disconnect switch shall be indicated in the immediate proximity of the electric service entrance. The disconnect switch shall be readily accessible for operation and locking by utility personnel in accordance with Section II.B of the NYSSIR, Operating Requirements. The disconnect switch must be lockable in the open position with a 3/8” shank utility padlock.

Central Hudson requires that the photovoltaic AC disconnecting means shall be installed at a readily accessible location on the outside of a building or structure, whether the meter is located inside or outside.  The location of the disconnect switch shall be within 10 feet of the utility’s external meter. If the meter is located on the inside of a building or structure, the AC disconnect switch shall be in immediate proximity of where the utility electric service entrance enters the building.  If this AC disconnect switch is not visible from the utility meter, a plaque shall be located at the utility meter indicating the presence and location of this AC disconnect switch.

* Any variations to the above requirements must be requested in writing, prior to preliminary construction approval. Only with written approval may the customer’s installation deviate from Company standards.

Generators greater than 5MW in size

Generators greater than 5MW in size are subject to Central Hudson’s Interconnection Requirements, as well as additional state and federal procedures, where applicable. Please refer to the following procedural and technical requirements for additional information: