Description
The GE Multilin 489-P5-LO-A20 is a microprocessor-based relay designed for the protection and management of small-to-medium-sized synchronous and induction generators. Part of the established 489 series, this specific configuration provides essential protection features including stator differential, overexcitation, and frequency monitoring, while managing thermal modeling to prevent insulation degradation.
Order Code Breakdown (489-P5-LO-A20)
- 489: Base unit for Generator Protection.
- P5: 5 A Phase CT secondary inputs.
- LO: Low Voltage control power supply (Range: 24–60 V DC; 20–48 V AC at 50/60 Hz).
- A20: Standard configuration with 4–20 mA analog outputs and basic communication options.
Availability and Procurement
- Condition: New Original (New Surplus) or Refurbished (Fully Tested)
- Warranty: 12-month technical replacement warranty
- Lead Time: Ready for immediate dispatch; global shipping available via DHL/FedEx
- Pricing: Price is subject to current market availability for legacy GE Multilin components. Contact our sales engineering team for a formal quote.
Technical Specifications
The 489-P5-LO-A20 integrates protection, monitoring, and metering into a single 19-inch rack or panel-mount chassis.
| Parameter | Value / Specification |
| Phase Current Inputs | 5 A secondary (Requires external CTs) |
| Control Power (LO) | 24–60 V DC or 20–48 V AC |
| Analog Outputs | 4 channels of 4–20 mA (User-configurable) |
| Frequency Tracking | 20 to 70 Hz (Supports 50 and 60 Hz systems) |
| Relay Outputs | 6 Output relays (Form C) |
| Digital Inputs | 9 Configurable inputs |
| Communication | RS232 (Front), RS485/RS422 (Rear); Modbus RTU protocol |
| Operating Temperature | −40 to +60 °C (−40 to +140 °F) |
Core Protection Functions (ANSI Device Numbers)
This module provides a comprehensive suite of protection elements defined by IEEE/ANSI C37.2 standards:
- 87G: Generator Stator Differential
- 49: Thermal Overload (RTU or Current-based)
- 32: Reverse Power (Anti-motoring)
- 40: Loss of Excitation (Field Failure)
- 24: Volts Per Hertz (Overexcitation)
- 51V: Voltage Restrained Overcurrent
- 46: Phase Unbalance (Negative Sequence)
Engineering Insights: Installation and Trade-offs
In my experience commissioning GE 489 units in peaking plants and industrial co-generation facilities, several factors are critical for reliable operation:
1. Power Supply Sensitivity
The “LO” power supply variant is designed for battery-backed DC systems (24 V or 48 V). If your facility uses 110/220 V DC station power, this module will be damaged upon energization. Verify the station battery voltage before connecting the power terminals.
2. CT Saturation and 5 A Inputs
The P5 designation means the relay expects a 5 A secondary from your Current Transformers. Ensure your CT classes (e.g., 10P20 or C400) are sized correctly for the maximum fault current. Using a 5 A relay on a 1 A CT circuit will result in a 5:1 metering error and potential failure to trip during a fault.
3. RTU vs. Thermal Modeling
For critical generators, I recommend using the RTD inputs (if equipped) rather than relying solely on the current-based thermal model. The 489 allows for “Thermal Modeling with RTD Feedback,” which provides a much more accurate representation of the stator winding temperature during high ambient conditions.
4. Communication Latency
The RS485 Modbus RTU interface on this unit is reliable but limited in bandwidth compared to modern IEC 61850 Ethernet relays. When polling the 489 for SCADA, limit the number of registers per request to maintain a scan rate below 500 ms.
FAQ
Q: Can I upgrade the firmware on an existing 489-P5-LO-A20?
A: Yes, but firmware updates on the 489 series must be done via the front RS232 port using GE EnerVista software. Ensure you back up your setpoint (.489) file first, as firmware jumps can occasionally reset user logic.
Q: Does this unit include the 10-channel RTD module?
A: The base 489-P5-LO-A20 typically supports RTD inputs, but you must verify if the specific unit has the RTD hardware installed on the rear terminal block. Check the physical terminal labels for RTD1 through RTD10.
Q: Is the 489-P5-LO-A20 interchangeable with the 489-P1-LO-A20?
A: No. The P1 version is for 1 A CT secondaries. Replacing a P1 with a P5 without changing the external CTs will result in the relay under-reporting current by 80%, creating a dangerous “fail-to-trip” condition.
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