Important Information for Technical Specialists and Partners!

Based on the technical condition monitoring of switching equipment and failure rate analysis over the last 18 months, a significant increase (over 40%) in operational failures has been recorded for Control Units operating on AC auxiliary power. This applies to the following models: BP(BU)/TEL-02/05A, CM/TEL-100/220-12-01/02/03А, CM16_1, and CM16_2 (hereinafter referred to as the EQUIPMENT).

Root Cause Analysis and Existing Solutions

The primary cause of damage is the substantial exceeding of maximum operating voltage levels from auxiliary AC power sources at substations and power supply facilities (without battery backup). Actual voltage levels frequently exceed not only the regulatory limits (253 V) but also the design thresholds of the EQUIPMENT (265–275 V). In some fault conditions involving intermittent ground faults, overvoltages exceeding 350 V of unpredictable duration occur.

Existing protection methods have proven insufficient under these conditions:

• 220/220 V isolation transformers do not reduce the voltage to a safe level.
• 220/100(110) V step-down transformers are not designed for continuous operation under overload conditions (exceeding 50%).

Revised Connection Recommendations

Given the non-standard voltage levels of 230 V nominal AC auxiliary power sources (without battery backup), it is recommended to connect the EQUIPMENT via single-phase voltage transformers utilizing a line-to-line voltage scheme.

Key Technical Specifications for Required Transformers:

• Rated Power: Not less than 63 VA.
• Primary Winding Rated Voltage: 380–400 V.
• Secondary Winding Rated Voltage: 230 V.

Ingress Protection (IP) Rating for Switchgear Enclosures:

• For protection and control compartments (anti-condensation design): Min. IP30.
• For protection and control compartments (condensing environments): Min. IP66.

This proposed power circuit configuration ensures stable operation of the EQUIPMENT within a wide input voltage range—from 150 V to 350 V.