Chapter 4: Guaranteed Operating Characteristic

IMPORTANT: Installers are required to ensure that all equipment proposed have the capabilities to implement all the requirements of the MSDG Grid Codes, especially requirements stipulated in this chapter.

4.1 Fault Ride Through Requirements

The MSDG shall remain connected to the distribution system for system voltage dips on any or all phases, where the distribution system voltage measured at the point of common coupling to the CEB network remains above the specified voltage duration profile.

Key Requirements:

During the distribution system voltage dip, the MSDG shall provide active power in proportion to retained voltage and maximise reactive current to the distribution system
The maximisation of reactive current shall continue for at least 3 seconds or until the distribution System Voltage recovers
Due to the dynamic nature of the distribution network, higher or lower fault clearance time and the LVRT voltage curve for the MSDG may be required

4.2 Frequency Response

In case of frequency deviations in the CEB network, the MSDG shall be designed to be capable to provide power-frequency response in order to contribute to the stabilisation of the grid frequency.

Requirements for MSDG ≥ 1 MW:

Operate with normal active power output under normal system frequency ranges
Reduce power output above a system frequency of 50.5 Hz
Power must be reduced with a gradient of 40% per Hz of the instantaneously available power
Output power only allowed to increase again when frequency is at 50.05 Hz
Disconnect within 0.5 seconds if frequency is above 52 Hz
Allowed to disconnect if frequency is below 47 Hz for longer than 0.5 seconds

4.3 Reactive Power Capability

MSDGs of capacity equal to or greater than 1 MW shall be equipped with reactive power control functions capable of controlling the reactive power supplied by the MSDG at the point of common coupling with CEB's network.

Control Functions (mutually exclusive):

Power Factor Control
Reactive Power Control
Voltage Control mode (if previously agreed with CEB)

Design Requirement: MSDGs of capacity equal to or greater than 200 kW shall be designed with the capability to supply rated power (MW) for power factors ranging between 0.95 lagging and 0.95 leading, available from 20% of rated power measured.

4.4 Power Quality

4.4.1 Limitation of Voltage Flicker

The MSDG installation shall not cause abnormal flicker beyond the limits defined in IEEE 519.

4.4.2 Harmonics

The MSDG system output should have low current-distortion levels to ensure that no adverse effects are caused to other equipment connected to the utility system. The MSDG system electrical output at the PCC should comply with IEEE 519.

4.4.3 Voltage Step Change

Step voltage changes caused by the connection and disconnection of generating plants at the distribution level should not exceed:

+/- 3% for infrequent planned switching events or outages
+/-6% of the nominal voltage of 22kV for unplanned outages such as faults

4.4.4 Surge Withstand Capability

The interconnection system shall have a surge withstand capability, both oscillatory and fast transient, in accordance with IEC 62305-3. The design of control systems shall meet or exceed the surge withstand capability requirements of IEEE C37.90.

4.4.5 Voltage Unbalance

The contribution to the level of unbalance of the voltage at the point of common coupling of any installation with generation should be less than or equal to 1.3%.

4.5 Ramp Rate Limits

MSDG of capacity equal to or greater than 1 MW shall have ramp up/down in normal conditions, positive ramp rate only during start-up and negative ramp rate during shut down of the MSDG facility, as follows:

1 minute maximum ramp rate: MSDG's installed capacity (MW) divided by 5

The ramp rate settings shall be approved by CEB prior to testing and commissioning of the system on the network. For any subsequent change, a minimum of two weeks' notice shall be given. Implementation by the Promoter shall be done within two weeks of formal request.