AFR 1xx, AFR 31 — ferroresonance suppression devices for voltage transformers
AFR 1xx and AFR 31 are intelligent loads for protecting instrument voltage transformers against ferroresonance in MV distribution networks. Unlike permanently connected damping resistors, AFR is activated only during ferroresonance and does not load the measuring windings in normal operation. The devices are installed in VT cells of 6–35 kV switchgear.
- Purpose
- protection of instrument VTs against ferroresonance in MV distribution networks
- AFR 11x
- for separately operating VTs (single-phase measurement, supply from MV)
- AFR 13x
- for the open delta circuit of auxiliary windings of three VTs
- Rated voltage
- 100, 110, 120, 100/√3, 110/√3, 120/√3 V AC (and others on request)
Price, availability and lead time on request. We help with analogue selection, customs clearance and delivery.
Description
Ferroresonance occurs between the inductance of the voltage transformer and the capacitance of the line or MV switching devices. It is triggered by switching on, switching off, earth faults and other transients. The VT core saturates, significant overvoltages and current peaks appear, and the transformer is most often destroyed. The highest risk is in networks with an isolated neutral and in cable networks.
AFR 11x is intended for separately operating transformers, that is for single-phase measurement or supply from the MV network. AFR 13x and AFR 31 are connected in the open delta circuit of the auxiliary secondary windings of three transformers. Rated voltage is 100, 110, 120, 100/√3, 110/√3 or 120/√3 V AC, other values on request. The circuit is protected by a B16A circuit breaker or an equivalent fuse.
In AFR 31 the activation voltage is set by a jumper to 20, 25 or 30 V, the factory value is 25 V. A higher setting is chosen for MV networks with greater asymmetry of stray capacitances. A delayed operation circuit (4 s as standard, adjustable at the factory from 0 to 10 s) coordinates the device with earth fault protection. This is needed when the same VT supplies earth fault monitoring and auto-reclosing. Parallel connection of AFR 31 does not affect the operation of the earth fault protection relay. The device is mounted on a 35 mm DIN rail, connected with flexible insulated wire up to 2.5 mm² and used indoors only.
In the same accessory group the company offers a TR305 damping resistor 68 Ω / 200 W for high-voltage instrument VTs. It is connected in the open delta and mounted horizontally or vertically. If the power consumption of the resistor interferes with the operation of a parallel protection or signalling relay, two resistors are connected in series.
Operation, installation and maintenance of AFR are performed by qualified personnel only. Before any work the transformers are disconnected from the network, and using the device without its cover is prohibited. One pole of the load is earthed, and before connection it is checked that the earthing is not made twice, on the transformer side and on the load side, because this would cause a short circuit on the instrument VTs. Manuals AFR111–AFR131 and AFR-31 are published for both types.
Technical specifications
| Purpose | protection of instrument VTs against ferroresonance in MV distribution networks |
|---|---|
| AFR 11x | for separately operating VTs (single-phase measurement, supply from MV) |
| AFR 13x | for the open delta circuit of auxiliary windings of three VTs |
| Rated voltage | 100, 110, 120, 100/√3, 110/√3, 120/√3 V AC (and others on request) |
| Principle | activated only when ferroresonance occurs |
| Circuit protection | B16A circuit breaker or equivalent fuse |
| TR305 resistor | 68 Ω, 200 W, for VTs |
Request a price and lead time
AFR 1xx, AFR 31 — ferroresonance suppression devices for voltage transformers. We reply within one business day.
Or email sales@usk.ua or call 044 339-50-20.
Customs codes
| UKTZED (Ukraine) | 8543 70 90 00 8533 29 00 00 |
|---|---|
| HS, 6 digits | 8543 70 8533 29 |
| CN (EU) | 8543 70 90 8533 29 00 |
| HTSUS (USA) | 8543 70 99 60 8533 29 00 00 |
| China customs tariff | 8543 70 99 90 8533 29 00 00 |
Codes are for reference: the final code is determined at declaration for the specific model.
Questions and answers
How does AFR differ from a damping resistor?
AFR is activated only during ferroresonance and does not load the VT windings in normal operation. Damping resistors, including TR305 68 Ω / 200 W, are connected permanently.
Which model should be chosen for an open delta circuit?
AFR 13x and AFR 31 are intended for the open delta of auxiliary windings of three VTs. AFR 11x is installed on separately operating transformers.
What rated voltage are AFR devices made for?
For 100, 110, 120, 100/√3, 110/√3 or 120/√3 V AC, other values on request. The circuit is protected by a B16A circuit breaker.
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