Certification and Protection Requirements

The interconnection process in Massachusetts specifies certain certification and protection requirements for distributed generation interconnected to the electric grid. Following is a summary of these requirements.

For the full requirements and description of the rationale behind them, please refer to Section 4 of the interconnection tariff establishing the interconnection standards.

Requirements for All Systems

All systems applying for interconnection must use the following design considerations:

. Transient voltages should be evaluated in the design of the facility.
. Standard maximum instantaneous deviation in frequency should be considered in the design of the facility.
. All electricity flow across the point of common coupling (point where system connects to the electric grid) shall be in the form of single-phase or three-phase 60 Hz alternating current at a voltage class determined by mutual agreement of the customer and utility.
. Facilities over 1 MW must provide reactive capability as per NEPOOL requirements.

All systems and equipment must also adhere and/or be certified in accordance with the following national standards:

. IEEE Standard 519 on noise and harmonics
. IEEE Standard 1547 on interconnection for distributed resources
. UL Listing 1741 on inverters, converters, and charge controllers
. Solar photovoltaic facilities must meet IEEE Standard 929-2000 on recommended practice for utility interface of photovoltaic systems.

Simplified Review Requirements (For Qualified Inverter-Based Systems)

In addition to the requirements above, the utility may require an external disconnect switch for all inverter-based systems (e.g. solar) eligible for the simplified review process. Whether this protection is required or not will be determined during the utility's review. It is also important to note that inverter-based projects over 10 kW and projects of any size located on area networks are not eligible for the simplified review process.

Expedited / Standard Review Requirements (For All Other Systems)

All other systems must meet the following requirements:

. If a facility will not be exporting power, it must include one of the following: (1) a reverse power relay with mutually agreed upon delay intervals; (2) a minimum power function with mutually agreed upon delay intervals; or (3) other mutually agreeable approaches.
. Some larger systems may be required to meet NPCC protective relaying requirements and/or emergency operation criteria.
. The facility must include a disconnect switch.
. A direct transfer tripping system, if required by the customer or utility, must use equipment acceptable to the utility and may require use of dual channels.

Additional requirements for induction and synchronous generators (not inverter-based) are outlined in Section 4.2.4.2.2 through 4.2.4.2.4 on pages 28-30 of the interconnectiont tariff.

Other Requirements

. Standby generators do not require protective relays if the paralleling option is automatic and takes place for less than ½ of a second. An interrupting device with a ½ second timer is required as a fail-safe mechanism. Parallel operation must be prevented when the utility line is dead or out of phase with the generator. The control scheme for automatic paralleling must be submitted for utility review and approval before the generator can be interconnected.

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