The General Electric UR 8HH, also cataloged as the 8HH CT/VT module, operates as a dedicated hardware component for signal scaling and electrical parameter acquisition within Multilin Universal Relay (UR) platforms. This module provides the interface for 3-1A/5A phase current transformers (CTs) and 1A/5A ground CTs, converting high-magnitude system inputs into secondary-level signals suitable for protective relay processing.

Hardware Specifications

Backplane Bus Communication and Signal Calibration

The UR 8HH module interfaces with the relay backplane to transmit scaled analog currents and voltages to the digital processing core. Signal integrity is maintained through calibrated secondary windings, which ensure that phase and ground current vectors are accurately represented for protection algorithm execution. While the module is a passive scaling component, it requires precise software-based configuration via the EnerVista UR platform to define the CT/VT ratios and secondary tap settings, ensuring that the relay interprets system values correctly for protective tripping logic.

Frequently Asked Questions

Q: Is this module capable of auto-scaling current inputs based on system load?

A: No. The UR 8HH requires manual configuration of CT/VT ratios and primary/secondary tap settings via the EnerVista UR software to accurately scale the input signals for the relay’s processing logic.

Q: Can the UR 8HH be hot-swapped while the primary system current is flowing?

A: No. Any attempt to remove or install this module while CT circuits are carrying current will result in hazardous open-circuit voltages across the CT secondary terminals. Always short-circuit the CT inputs at the terminal blocks before servicing the module.

Field Installation Guidelines

1. Ensure the primary circuit is de-energized and the CT secondary circuits are shorted at the field junction box before handling the module.
2. Verify that the UR chassis is de-energized and all power sources are isolated.
3. Slide the UR 8HH into the designated slot, ensuring firm engagement with the internal backplane connectors.
4. Secure the module using the front-panel captive screws to maintain proper grounding and mechanical stability.
5. Connect CT/VT leads to the terminal blocks, ensuring torque specifications are met to prevent high-resistance connections.
6. Use the EnerVista UR software to verify scaling factors and signal values before placing the relay back into protective service.