GE UR8HH Universal Relay Combined CT and Digital I/O Module
The GE UR8HH, also cataloged as the UR-8HH Combined CT/VT and Digital I/O Module, operates as a dedicated hardware component for high-density current transformer sensing and discrete tripping control within GE Multilin Universal Relay (UR) platforms. The module captures three-phase and ground CT signal inputs while simultaneously monitoring 16 optically isolated digital input lines and driving 8 high-capacity Form-C output relay contacts.
Suffix Breakdown & Model Matrix
| Base Part Number | Ordering Suffix | Primary Function | Input Channels | Output Channels |
|---|---|---|---|---|
| UR8HH | UR-8HH | Combined CT & Digital I/O Module | 4 CT Channels (3 Phase, 1 Ground) + 16 Optically Isolated Digital Inputs | 8 Form-C Relay Outputs |
Hardware Specifications
| Parameter | Specification |
|---|---|
| Model | UR8HH |
| Brand | GE Multilin (General Electric) |
| Origin | USA |
| Weight | 2.27 kg |
| Dimensions | 170 mm x 105 mm x 32 mm |
| Operating Temp | -40 deg C to +85 deg C |
| Power Consumption | Power supplied via internal UR backplane bus |
| CT Input Rating | 3 Phase + 1 Ground (1 A or 5 A nominal, software-selectable) |
| Digital Inputs | 16 optically isolated channels (24 VDC to 250 VDC) |
| Relay Outputs | 8 Form-C (10 A at 250 VAC / 30 VDC) |
| Dielectric Strength | 2 kV AC for 1 minute (I/O to Ground) |
Backplane Bus Communication Velocity and Deterministic Control
The UR8HH module communicates with the central process module through the high-speed Universal Relay backplane bus, maintaining high backplane bus communication velocity during sub-cycle protective tripping algorithms. Internal analog-to-digital converters process phase and ground current waveforms synchronously, streaming raw sampling data across the internal bus without latency. This deterministic network interface allows the relay processing unit to process current differential or overcurrent conditions and trigger Form-C output contacts within millisecond timeframes.
Frequently Asked Questions
Q: Can the CT secondary current rating be changed in the field without hardware modification?
A: Yes, the 1 A or 5 A nominal CT rating for phase and ground channels is selected directly through the relay firmware setup software, requiring no physical jumper changes on the board.
Q: What is the isolation rating between the digital input terminals and the internal backplane bus?
A: The digital inputs feature optical isolation rated at 2 kV AC dielectric strength for 1 minute between the field terminals and system ground.
Q: Is this expansion module hot-swappable while the Universal Relay chassis is energized?
A: No, field engineers must fully isolate and de-energize the relay chassis and short the external CT secondary circuits before removing or inserting the module.
Field Installation Guidelines
Follow these standardized procedures when installing or replacing the module in a Universal Relay 6U chassis:
- De-energize the relay chassis power supply and apply shorting blocks to all active CT secondary circuits connected to the module rear terminals.
- Align the UR8HH board edges with the target 6U card guide slot in the Universal Relay chassis frame.
- Slide the card smoothly into the slot until the rear edge connector firmly seats into the backplane bus socket.
- Tighten top and bottom retaining thumbscrews on the front faceplate to ensure chassis ground continuity and mechanical stability.
- Connect CT current leads, digital input field wiring, and Form-C output control cables according to the panel terminal block map, keeping AC signal wiring separated from DC control leads.
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