MELPRO-A, digital protection relays for incomers and high-voltage distribution
MELPRO-A is a series of microprocessor protection relays for high-voltage incoming and distribution switchgear of consumers and distribution substations. The series includes overcurrent, directional and current-based earth fault, undervoltage, overvoltage and zero-sequence voltage relays. The new model is compatible with the previous series A in panel cut-out and settings.
- Models
- MOC-A3 (overcurrent, 50/51), MDG-A3/A4 (directional earth fault protection, 67G), MGR-A3 (current-based earth fault protection, 50G), MUV-A3 (27), MOV-A3 (59), MVG-A3/A4 (64/59G)
- Overcurrent
- 2 phases, 2 instantaneous and 4 inverse-time types, 3rd step 20–80 %
- DGR sensitivity
- Vo from 2 %
- Connection to ZVT MPD-3
- up to 20 DGR/OVGR relays
Price, availability and lead time on request. We help with analogue selection, customs clearance and delivery.
Description
The range consists of six relays. MOC-A3 provides two-phase overcurrent protection and has two types of instantaneous overcurrent element (code 50) and four types of inverse-time characteristic (code 51). MDG-A3/A4 is responsible for directional earth fault protection (67G), MGR-A3 for current-based earth fault protection (50G). The undervoltage relay MUV-A3 (27) and overvoltage relay MOV-A3 (59) work without a separate auxiliary supply. MVG-A3/A4 protects on zero-sequence voltage (64/59G).
In MOC-A3 a third step has been added to the instantaneous element. It operates at a current of 20–80 % of the instantaneous setting, selectable in 4 steps, and eases coordination of protection at distribution substations. In the earth fault relays the setting range is wider than in the previous model. The minimum zero-sequence voltage setting Vo of the directional DGR relay has been lowered to 2 %, so the protection is more sensitive to earth faults. Up to 20 DGR or OVGR relays can be connected to one zero-sequence voltage detector ZVT MPD-3, if the system is built only on MELPRO-A.
The relays comply with the current editions of the JEC and JIS standards, which were revised to take the characteristics of digital relays into account. The panel cut-out is the same as in the previous series A, so replacement requires no panel modification. The protection functions and settings of the new model are upward compatible with the previous one.
The selector switches have more convenient knobs, and the front panel labels are large and designed on the principles of universal design (UD). After a setting is changed, the LED indicator shows the new value with priority for about 3 s, which is convenient during relay checks. Continuous self-monitoring checks the inputs, power supply and processor. For MOC, MUV and MOV there is frequency mismatch monitoring, which warns if the set frequency differs from the input one. All models record and display values at the moment of operation, so fault analysis takes less time.
In the drawout version (RD) the relay unit is withdrawn from the case without disconnecting wires, which shortens maintenance work. For earth fault protection the manufacturer supplies zero-sequence voltage detectors and zero-sequence current transformers.
Technical specifications
| Models | MOC-A3 (overcurrent, 50/51), MDG-A3/A4 (directional earth fault protection, 67G), MGR-A3 (current-based earth fault protection, 50G), MUV-A3 (27), MOV-A3 (59), MVG-A3/A4 (64/59G) |
|---|---|
| Overcurrent | 2 phases, 2 instantaneous and 4 inverse-time types, 3rd step 20–80 % |
| DGR sensitivity | Vo from 2 % |
| Connection to ZVT MPD-3 | up to 20 DGR/OVGR relays |
| Design | drawout (RD) |
| Standards | JEC, JIS |
Request a price and lead time
MELPRO-A, digital protection relays for incomers and high-voltage distribution. We reply within one business day.
Or email sales@usk.ua or call 044 339-50-20.
Customs codes
| UKTZED (Ukraine) | 8536 49 00 00 |
|---|---|
| HS, 6 digits | 8536 49 |
| CN (EU) | 8536 49 00 |
| HTSUS (USA) | 8536 49 00 85 |
| China customs tariff | 8536 49 00 00 |
Codes are for reference: the final code is determined at declaration for the specific model.
Questions and answers
Which relays are in the MELPRO-A series?
MOC-A3 (50/51), MDG-A3/A4 (67G), MGR-A3 (50G), MUV-A3 (27), MOV-A3 (59) and MVG-A3/A4 (64/59G). The voltage relays MUV-A3 and MOV-A3 work without a separate auxiliary supply.
What is the sensitivity of directional earth fault protection?
The minimum zero-sequence voltage setting Vo of the DGR relay is 2 %. Up to 20 DGR or OVGR relays can be connected to one ZVT MPD-3 detector.
Can MELPRO-A replace relays of the previous series A?
Yes, the panel cut-out matches the previous series A, so no panel modification is needed. In the drawout version RD the relay unit is withdrawn without disconnecting wires.
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