CHP (WKK) installations — grid connection, protection and anti-islanding

A CHP installation (combined heat and power, in Dutch: WKK — warmtekrachtkoppeling) is almost a standard facility in Dutch greenhouse horticulture: a single gas engine simultaneously supplies heat, electricity, and — via the flue gases — CO2 for the crop. As soon as such a unit runs in parallel with the public low-voltage grid, additional requirements apply on top of the regular NEN 1010 installation requirements.

NEN-EN 50549-1: parallel operation with the grid

NEN-EN 50549-1 (revised 2019 edition, with amendment A1:2023) is the standard for generating installations that operate in parallel with the public low-voltage distribution grid. The standard sets requirements for, among other things:

• The permitted voltage and frequency range within which the CHP (WKK) unit must keep operating (ride-through), instead of tripping immediately on a brief deviation.
• The required active/reactive power response of the unit in the event of grid deviations.
• Mandatory anti-islanding protection: the unit must disconnect itself as soon as the grid drops out, to prevent the CHP (WKK) unit from continuing to feed part of the grid "in island operation" — a safety risk for grid-operator personnel working on a presumed de-energised network.

Note: whether specifically Part 1 (low voltage) or Part 2 (medium voltage, 1-35 kV) of NEN-EN 50549 applies depends on the actual connection voltage of the CHP (WKK) unit concerned — verify this per project with the grid operator rather than defaulting to low voltage.

Selectivity with the grid operator's protection

The protection settings of the CHP (WKK) unit must be selective relative to the grid operator's own protection at the connection point — comparable to the selectivity principle between installation protective devices (see the guide on selectivity), but here between the generating installation and the grid. In practice, the exact settings (type-test certificates, settings register) are not determined by NEN-EN 50549 alone, but in consultation with the Netcode Elektriciteit (Dutch grid code) and the specific requirements of the grid operator concerned at the actual connection point.

Notification duty to the grid operator

For a CHP (WKK) unit connected to, or forming part of, a low-voltage installation, prior approval from the grid operator is generally not required, but a notification duty within one month after commissioning does apply.

Note: the exact disconnection times for vector-shift/ROCOF-based anti-islanding protection are project-specific (depending on the type of protection relay and the grid operator's requirements at the connection point) and cannot be reduced to a single universal figure from freely accessible sources — request the current settings from the protection relay supplier or the grid operator.

Common mistakes

1. Treating NEN-EN 50549 as a replacement for the regular NEN 1010 installation requirements — the standard specifically governs parallel operation with the grid, on top of (not instead of) the installation requirements of NEN 1010.
2. Assuming anti-islanding protection is "automatically present" without having the settings certified/tested — the protection must be demonstrably configured and tested, not merely present from the factory.
3. Assuming a single fixed Part (1 or 2) of NEN-EN 50549 applies without checking the actual connection voltage — this differs per project and must be confirmed with the grid operator.
4. Forgetting the notification duty to the grid operator, or filing it too late — even without a prior-approval requirement, notification within one month of commissioning remains a standalone obligation.

Related

• Emergency Generators & Low-Voltage Generation — §551
• ATEX & explosion-hazard zones
• Distribution boards & selectivity between protective devices