Single-Phase MCR as Automatic Ground-Fault Neutralizer (Patented)

APPLICATION FIELD AND PURPOSE:

Neutralizes automatic ground-fault capacitive current in electrical networks with isolated neutral.

Prevents transition of single-phase ground faults to multi-phase short circuits.

COMPLETE EQUIPMENT:

• Electric reactor (2) with built-in thyristor converter, controlled by self-magnetization– 1 unit;
• System for ground fault capacitive current measurement and for automatic adjustment of reactor current (1) – 1 unit.
• Overvoltage limiter (5)– 1 unit.
• Optional 3-phase network connection filter (4)– 1 unit.
• Optional grounding transformer and voltage transformer (3)– 1 unit.

PRINCIPLES OF OPERATION:

In the figure shown, an automatic adjustment and control system (1) defines the expected value of ground fault capacitive current and sends a control signal to the single-phase MCR converter (2), thus providing reactor control.

When a ground fault occurs, the reactor reduces the resulting current value at the damage point to a negligible value. The reactor switches to compensation mode without requiring intervention by maintenance personnel. The adjustment process is fully automatic.

Under normal operating conditions, the single-phase MCR is not saturated, eliminating resonance overvoltages in the neutral line.

This reactor may also be used in 3-phase electric grids and consumers. In this case, a filter (4) for connection of the reactor to the 3-phase network is supplied with the reactor.

MAIN TECHNICAL DATA:

Rated power:	190 kVA	300 kVA	480 kVA	840 kVA
Rated voltage:	11/3 kV; 6.6/3 kV	11/3 kV; 6.6/3 kV	11/3 kV; 6.6/3 kV	11/3 kV
Frequency:	50(60) Hz	50(60) Hz	50(60) Hz	50(60) Hz
Compensation current control range (continuous mode):	2.5 to 25, 4.25 to 42.5	4.0 to 40, 6.6 to 60	6.3 to 63, 10.5 to 105	11 to 105
2 hour compensation mode current:	30 A 50 A	48 A 80 A	76 A 126 A	132 A
Residual current, phase-to-ground short circuit:	2.0 A 2.75 A	2.75 A 3.5 A	3.5 A 5.0 A	5.0 A
Dimensions:	1030x1165 x1690 mm	1100x1235 x1710 mm	1130x1410 x1750 mm	1160x1980 x1950 mm
Weight:	1200 kg	1750 kg	2000 kg	3500 kg
Oil weight:	250 kg	350 kg	450 kg	1000 kg
Special orders:	Any power up to 2.5 MVA, Any voltage up to 35 kV.

AUTOMATIC ADJUSTMENT & CONTROL SYSTEM

EFFICIENCY OF USE

Use of the single-phase MCR results in reduction of ground faults by a factor of three and their full containment in overvoltage-caused insulation breakdown.

This device provides intact operation and increased lifetime of electric equipment.

Average cost recovery has been achieved in about 2.5 years.

TOTAL COST OF OWNERSHIP (TCO)

As a percentage of ex-works price TCO is as follows:

In other words, the TCO of an MCR is similar to that of a transformer of the same class.

MEAN TIME BETWEEN FAILURE (MTBF)

CERC guarantees its MCR's for a lifetime of not less than 25 years, with first major maintenance guaranteed not to occur within 12 years.

Each phase of the reactor, its grounding filter and current-distortion corrector (an LC filter) are guaranteed for a minimum of 3 years.

The power control system, including the transformer with its built-in thyristor subsystem is guaranteed for one year. The average practical time to failure of smaller MCR's is 5 years.