Schweitzer SEL C70TC3HKHF8NH6DM8VP67U67W67 SEL-70TC Transformer Protection Relay Unit

Module Feature

C70TC3HKHF8NH6DM8VP67U67W67 is a member of Schweitzer SEL-70TC series transformer protection relay. It implements restrained transformer differential protection as its core element, plus backup phase and ground overcurrent, overvoltage, undervoltage, overexcitation and thermal protection functions. The relay supports flexible logic programming, configurable digital and analog I/O, multiple communication ports including Ethernet, SEL Mirrored Bits, DNP3 and IEC 61850 optional. It provides fault event recording, oscillography, metering and breaker control capability. It is widely deployed in utility substations, industrial power plants and renewable energy collector systems for two-winding and three-winding power transformers.

Working principle

CT secondary currents from transformer primary and secondary windings are sampled continuously. The relay calculates differential and restraint currents to identify internal transformer faults while restraining for through-load and external fault conditions. All protection elements run in parallel with metering, control and disturbance recording functions. Upon trip condition, output contacts operate to open associated breakers and record fault waveform and event sequence data.

Onboard components

Main DSP processor board, CT/PT input conditioning board, power supply module, contact output driver board, communication interface module, local HMI display and keypad, time synchronization circuit.

LED indicators

Front panel LEDs indicate power, relay healthy, trip status, alarm and communication port activity.

Hardware self‑diagnosis

Continuous self-monitoring. Detects power supply failure, analog input anomaly, memory error, communication interruption and internal hardware fault, asserts alarm and blocks protection if critical failure occurs.

Programming software

SEL AcSELerator QuickSet, used for relay setting, logic editing, oscillography review, event log analysis and firmware upgrade.

Electrical & Process Parameters

Model:C70TC3HKHF8NH6DM8VP67U67W67 Brand:Schweitzer SEL Device type:Transformer Protection Relay Inputs:AC current and voltage Protection core:Transformer differential protection Function:Transformer fault protection, metering, breaker control and disturbance recording

Mechanical & Structure

Mounting:Panel rack mount Protection class:IP40 front bezel Housing:Metal relay chassis

Environmental

Operating temperature:-40℃ ~ +85℃ Storage temperature:-40℃ ~ +85℃ Ambient humidity:5~95% non‑condensing Certification:IEEE, IEC, UL, CE compliant Status:Schweitzer SEL original protection relay spare

Installation

Install relay inside control panel, wire CT circuits with shorting blocks in place before energizing CTs. Set transformer ratio, vector group and protection thresholds, then perform differential test and communication commissioning. Sync time source for event timestamp consistency.

Interface

CT/PT analog input terminals, binary input terminals, trip and auxiliary output contacts, Ethernet ports, serial communication port, IRIG-B time sync port.

Diagnostic

Differential current alarm: CT wiring polarity error, CT saturation, tap changer mismatch, internal winding fault. Spurious trip: Incorrect restraint setting, CT open circuit. No communication: Network cable fault, IP address conflict, port configuration mismatch. Oscillography missing: Fault recording trigger logic not properly configured.

Product BriefSchweitzer SEL C70TC3HKHF8NH6DM8VP67U67W67 SEL-70TC transformer differential protection relay, multi-protection element with oscillography and IEC 61850 optional, for substation transformer protection and control.