The Neutral  Grounding Resistors are generally employed in the LV and MV distribution networks to protect power transformers and generators from damaging currents in the event of earth fault. This protection system represents the best choice in terms of fast response to localize the fault and consequently to reduce and prevent the overheating and mechanical stress on the conductors.

Alternative protection systems like insulated neutral or direct earthing neutral  have several and significant disadvantages such as dangerous transient over-voltages and high difficulties to localize the ground fault in the insulated systems or damaging fault currents with possible arc blast  in the earthing neutral  systems.

By inserting the Neutral Grounding Resistors with appropriate characteristics between the neutral point of the transformer and the ground it is possible to limit the ground fault current for a short time to allow a quick localization of the fault but, at the same time, it does not damage the equipment.

The advantages of this solution are:

to limit the damages to the electrical equipment, such as switch-gear, transformers, cable and rotating machine and to prevent the extension of the fault with benefit also for the safety of the personnel

to protect the conductors and the system equipment from overheating and mechanical stresses

In many low and medium voltage systems, the system neutral may not be available. This is specifically true on Delta and ungrounded Wye Connected  systems. To be able to ground these systems, grounding transformer (Zigzag or Wye-Delta type) can be used to create a neutral, which in turn can be connected to ground either directly, or more commonly, through a Neutral Grounding Resistor. These combinations are known as artificial neutrals and in each of them is possible to install a Neutral Grounding resistor.

The resistors must absorb a great energy for very  short time, few seconds, and as components of the security system they must assure a high reliability. For this reason it is fundamental design them  optimizing the weight of active material (stainless steel) of the resistor elements according to the maximum acceptable heating over temperatures.

Each PEW Neutral Grounding Resistor is designed and manufactured to meet the technical specifications issued by the customer.

The main features and characteristics of the product are:

• Resistor elements in stainless steel coil type with high thermal capacity

• Rated currents up to 10 kA

• Insulation level from 1 kV to 132 kV

• Protection class from IP00, for indoor installations, to complete IP55 solutions for outdoor applications

• Painted enclosures or as alternative mild galvanized, stainless steel

Many optional features/equipment can be associated with the Neutral Grounding Resistors:

• Terminal box for I/O cables

• Terminal box for additional devices

• Zigzag grounding transformer, dry type, air cooled

• Three phase transformer Wye / Delta type

• Current and/or Voltage transformers

• Earth fault Relay

• Load-break or load-less load switches

• Vacuum contactors

• Surge arrestor

• Space heater

Accessories:

• Resistance elements

• Insulators

Optional:

• Isolators (Manual/Motorized)

• Vacuum Contactor with different operating voltages

• Neutral Current Transformer

• Monitoring Relay with wide range of options

• CBCT

• System Voltage(VL)-(LL)

• Limiting Current

• Resistance Value

• Time Duration

• Temperature Rise

• **CT detail, if required

• **Protection relays detail, if required

• ** Isolator / VCB detail, if required

• ** any other specific requirement

Do’s:

• Place/Use it as per the enclosure's IP ratings.

Don’ts: