1.1   Scope of Application

MRD-FD type neutral ground resistor cabinet is complete equipment specially used by generators in power plant which adopts high-resistance grounding for neutral. The voltage grade for generator mainly ranges from 6kv to 20kv. When one point of the stator grounds, the devices is able to limit the grounding current at a reasonable value and effectively restraint arc flash transient overvoltage associated with single-phase grounding.

1.2   Operation Environment

1. Applies to indoors.
2. Ambient temperature: between -40 and +40 centigrade
3. The altitude shall not exceed 3000m.
4. Relative humidity be or lower than 95% (25centigrade)
5. Power grid frequency: 58-62Hz (60Hz System), 48-52Hz (50Hz System)
6. The air at the installation site shall be free from chemical corrosion, vapor or explosive dust.

2.         Product Model Description

According to user's requirement, service of calculation resistance value and determining model No. is free.

2.1   Parameters of Grounding Transformer

Insulation class: H

Temperature rise: ≤100K

Cooling: AN

Protection Level: for paper-insulated dry type grounding transformer, the PI is divided into IP00 (no enclosure), IP20, and IP23 (with enclosure).

Insulation level, impedance voltage on-load loss and no-load loss are according to relevant national standards.

Insulation resistance testing: high voltage-low voltage and to earth ≥300MΩ, and low voltage-earth≥100MΩ.

3.         Structure of Complete Device

3.1   Composed Elements

Dry type single-phase grounding transformer, resistor, disconnector, surge arrestor and so on.

CT is also equipped in the enclosure which measures neutral current and outputs analog quantity.

3.2   Recommended Technical Parameters of MRD-FD Type Generator Neutral Resistor

If the parameters of project is not within above table or need more accurate data, we could calculate according to actual project.

In the table primary side voltages of grounding transformer with brackets are for line voltage, and the other ones are for phase voltage. And so is the secondary side resistance.

4.         Diagram of Installation and Wiring

The cabinet body is made of coated cold rolled steel or stainless steel. Wiring is led-in through wall bushing on the top or by cable at the bottom of enclosure.

Note: The enclosure should be reliable grounding

5.         Ordering instructions

Please provide the following information when place the order

Generator rated voltage, grounding transformer transformation ratio and resistance

Grounding transformer insulation form (dry or oil-immersed)

Current transformer transformation ratio

Wiring-in from the top or bottom

Time of fault current flowing-through

Material, IP and color of enclosure and installation site