Power Resistors

 
Neutral Grounding Resistors

 

Neutral Grounding Resistors (NGRs) are utilized to restrict fault currents, ensuring the safety of both equipment and personnel within industrial systems. Positioned between the neutral point and ground, NGRs elevate the overall resistance in case of an earth fault, thus constraining the current to a secure magnitude.


General Features

 

  • Stainless-steel resistor elements

  • Current transformers included (EN 61869-2)

  • Bolted resistor element connections instead of welded connections providing the possibility for immediate assembly of spare parts on site

  • Typically hot dip galvanized steel enclosure (painted or stainless steel enclosures are available on demand)

  • Stainless steel lifting eyebolts

  • Rugged shock-resistant construction (IK10)

  • Solid top cover sloped to prevent water accumulation

  • Corrosion resistant stainless steel nameplate

  • Exproof (ATEX) options available on demand

 

Technical Specifications

 

  • Operation Voltage: Up to 110 kV line to systems

  • Rated Current: Up to 5000 A

  • Ambient Temperature: Up to 55 °C (For higher ambient temperature, consult factory)

  • Resistance Alloy: Stainless-steel (CrNi or CrAl)

  • Protection Degree: IP 23 (outdoor) and others on demand

  • Standards: IEEE C57.32, IEC 60076-25, IEC 60137 & 60273, EN ISO 1461, EN 10346, ISO 12944, IEC 60071, IEC 60060, IEC 60529

 

Harmonic Filter Resistors

 

All harmonic filter resistors are tailor-made for diverse applications. During design stage, multiple factors, including voltage, current, inductance, size, and loss characteristics are taken into account to ensure the most efficient design at competitive prices

 

Dynamic Breaking Resistors

 

Advantages

 

  • Manufactured for any power rating and duty cycle

  • Galvanized, stainless steel or aluminum case enclosed models

  • Custom designs available in addition to standard modules

  • Suitable for any brand and model of Variable Frequency Drives (VFDs)

  • For high continuous powers and areas where space is a limitation, fan cooled braking resistors are also manufactured especially for marine, mining, and traction sectors.

 

Breaking Chopper for External Resistors

 

  • Input voltage: 650 VDC

  • Suitable drive voltage: 400 VAC

  • Suitable drive power: 2.2-100 kW

  • Rated continuous current: 40 A

  • Rated pulse current ( ED=10% ): 200 A

  • Rated continuous power: 26 kW

  • Rated pulse power ( ED=10% ): 130 kW

  • Minimum resistance value: 3.1 Ohm

  • Ambient conditions: -10 to 40 °C, max. 1000m altitude

  • Storage temperature: -25 to 70 °C

  • Dimensions ( WxHxD ): 209,2 mm x 293,4mm x 146,9mm

  • Weight: 4 kg

  • Protection degree: IP 20, EN 60529

  • Parallel Operation: Up to 7 modules, approx. 1000kW peak braking power

 

Anti Condensation Heaters

 

Anti-Condensation Space Heaters are engineered to uphold the temperature within an electrical enclosure at a desired level. Their purpose is twofold: to eliminate water vapor present inside enclosures and to prevent frost formation by maintaining the internal temperature above freezing. These heaters operate through convection, effectively preventing condensation buildup.

 

Features 

  • Operating Voltage: 24 - 690 V AC / DC

  • Rated Power: 15 - 150 W

  • Heater Body: Extruded aluminum profile or stainless steel

  • Mounting position: Horizontal or Vertical

  • High Performance in polluted areas

  • DIN Rail mount or flat surface mount

  • 35 mm DIN rail clip (HR.A, Hry and PTC series)

  • Other voltage / power output options upon request

  • High reliability

  • Natural convection

  • Durable construction

 

Neutral Grounding Resistors

 

Neutral Grounding Resistors (NGRs) are used to limit the fault current and ensure safety of equipment and personnel in industrial systems.

 

In solid grounding, the system is directly grounded and the fault current is limited only by the soil resistance. The fault current can be very high which can damage the transformers, generators, motors, wiring and other equipments in the system. NGRs are inserted between neutral and ground in order to increase the net resistance in the event of an earth fault and limit the current to a safe level.

 

Advantages of NGRs include:

 

  • Reduce the single phase fault currents and secure each piece of equipment in MV electrical networks,

  • Reduce the transient overvoltages which can occur during an earth fault, and be monitored and used to activate the earth fault relay,

  • Increase protection of generators, transformers and related equipment,

  • Reduced operation/maintenance costs,

  • Increase safety,

  • Provide simple, reliable, selective means of protection,

  • Allows the use of equipment, and in particular cables with lower insulation levels than for an insulated neutral scenario

  • Reduce the step voltage

 

The fault current value should be limited to a value that can be safely handled by the machine or transformer. It also needs to be high enough to be sensed by the earth fault protection relays. If the NGR resistance value is too high, the fault current will be very low and will not be able to activate the earth fault protection relay during earth fault conditions.

 

In a three phase star connection, the capacitances are formed with the ground. In the event of an earth fault, these capacitances may get charged with the line voltage and may cause transient overvoltages. The NGR should have a value that permits a let-through current which enables the capacitances to discharge.

 

The resistances are also categorized by the time that they can withstand the fault current. Typical durations are 5-10 seconds. The extended time rating resistors are used in systems where the reliability of the system is critical, e.g. petroleum industries, mines, etc. In these situations, high resistances are used for withstanding long periods of earth fault. When an earth fault occurs in one phase, an alarm will be generated. However, the system continues to run until the next scheduled shutdown.

 

Hilkar Neutral Earthing Resistors are designed to absorb a large amount of energy without exceeding temperature limitations defined in IEEE 32. Hilkar NGRs can be used in both indoor and outdoor settings. The neutral point is connected with a porcelain bushing or a high voltage (XLPE) cable, typically (minimum cross-section = 70mm2 copper or 95mm2 aluminium) from the bottom, top or side. The most common protection degree preferred for NGRs is IP 23 as it allows the resistor elements to cool more easily. Because the resistor elements are comprised completely of stainless steel, they are capable of withstanding extreme environmental conditions and thus suitable for both the seashore and desert. NGRs are shipped with maintenance and installation guidelines which include recommended relay settings. Hilkar provides complete technical assistance in order to meet your specifications or site conditions.

 

NGR Options

 

  • Elevated support stands are provided for ground clearance and safety

  • Specially designed units for hazardous and extreme locations (Ex-proof, ATEX certified)

  • Stainless steel or aluminium enclosures on demand

  • Installation of voltage transformers

  • Installation of protection relays

  • Porcelain entrance bushings can be mounted on the top or on the side of enclosure

  • Grounding transformer installation

  • Motorized or manual single pole disconnector switches, load break switches, vacuum contactors, circuit breakers, surge arresters and heaters in the Neutral Grounding Resistors

 

General Features

 

  • Stainless-steel resistor elements

  • Current transformer included (EN 61869-2)

  • Bolted resistor element connections instead of welded connections providing the possibility for immediate assembly of spare parts on site

  • Painted on demand

  • Typically 2 mm hot dip galvanized steel enclosure

  • High thermal capacity to absorb high currents

  • High altitude ratings

  • Custom made lifting eyes to ensure secure lifting

  • Rugged shock-resistant construction

  • Solid top cover sloped to prevent water accumulation

  • Corrosion resistant stainless steel nameplate

 

Technical Specifications

 

  • Operation Voltage : Up to 110 kV line to line systems

  • Rated Current : Up to 5000 A

  • Ambient Temperature : Up to 55oC (For higher ambient temperature, consult factory)

  • Resistance Alloy : Stainless-steel (CrNi or CrAl)

  • Protection Degree : IP 23 (outdoor) and others on demand

  • Standards : IEEE 32, IEC 60137 & 60273, EN ISO 1461, EN 10346, EN 12 ISO 129 44, IEC 60071, IEC 60060, IEC 60529

 

Routine Tests

 

  • Measurement of insulation resistance between enclosure and resistor

  • Measurement of DC resistance

  • Insulation test of resistor blocks

  • Thickness measurement of galvanization and/or paint

 

Type Tests

 

  • Temperature rise test

  • Protection degree test

  • Impulse voltage test (1.2 / 50 µs)

 

Special Tests (on demand)

 

  • Measurement of AC resistance

  • Seismic test

  • Insulation resistance test (Megger)

 

Selection Details

 

  • System Voltage (kV)

  • Line to Neutral Voltage (kV)

  • Desired Current Rating (A)

  • Desired Resistance Value (ohm)

  • Maximum Time ON (seconds) and duty cycle

  • Bushing Entry or Cable Entry

  • Current Transformer Ratings (if applicable)

  • Disconnector Switch (if applicable)

  • Special Options (if applicable)

 

High Resistance Neutral Grounding Devices

 

The design and operation of 240-5000 V systems, service continuity, personnel and equipment safety are the most important aspects in industrial systems. The use of the high-resistance grounded (HRG) system can provide a safe, reliable and economic system for 240-5000 V networks.

 

HRG systems limit the fault current by placing high resistance between neutral point of transformer (or generator) and ground. As it is not possible to locate the fault point in delta connected systems, an artificial neutral point is created and delta connected system can be grounded. This allows a fault current of a few amperes thus locating the fault point gets easy. When the neutral point is grounded thru high resistance, both continuity of operation is provided during fault condition and sufficient current (typically between 2 A and 10 A) flow is provided for ease of locating the fault point.

 

Approximate phase to earth fault current in 240-5000 V networks are:

 

  • Solidly grounded systems : 1000-6000 A
  • Low resistance grounded systems: 100-1000 A
  • High resistance grounded systems: 2-10 A
  • Ungrounded (or delta) cable system: 0.3-2.8 A/km: 2-10 A

 

General Features

 

  • 0-10 A analog ammeter, 0-250 V analog voltmeter with setting on panel
  • Automatic door switch for power shut down
  • Test button to indicate fault
  • Green light for normal conditions
  • Intermittent alarm and red light during ground fault
  • Pulse/Normal Selector swith to magnify current and intermittent pulse during ground fault
  • Auxiliary free contacts at pulse and alarm position during fault
  • Dimensions (LxWxH)= 60 x 60 x 180 cm (Other enclosure types avaible on demand)
  • Suitable for 240-5000 V three phase systems
  • Optional data logging

 

Usage

 

While locating the ground contact point of phase and ground, a fault current that is limited to approximately 2A, generating approximately 10A pulses (approx. 1 second on, 1 second off) provides ease of measurement. Thus using short time pulses is the common application in HRG systems today.

 

Measurements are generally taken by analogue and wide clamp ammeters. The clamp ammeter outside the phase cable is traced until the pulse current disappears on the analogue display.

 

High Resistance Grounding Systems are economical and practical choice especially for systems under 5000 Volts.

As zero sequence currents (3Io) flow thru neutral point due to line capacitance of cables, HGR alarm level is set to a point that is greater than 3Io.

 

 

 

Generator Neutral Grounding & Leads Cubicles

 

Generator Neutral Grounding Cubicles are designed to minimize fault damage incurred by generators, maintain sufficient fault detection and improve power system reliability. Generator Neutral Grounding and Lead Cubicles are manufactured according to IEEE or IEC standards.

 

Features

 

  • Up to 17.5 kV 5000 A
  • Test terminals for current and voltage transformers secondaries
  • Circuit diagram included in terminal box
  • 100 W anti-condensation heater included against condensation
  • Zinc-oxide lightning arresters and surge capacitors on demand
  • Voltage transformer fuses with signal contacts
  • MV fuse protection
  • Metal enclosed panels
  • Type tested panels

 

Generator Neutral Grounding Cubicles

 

  • 3 pcs. current transformers
  • 1 pc. neutral current transformer
  • 1 pc. neutral current ammeter
  • 1 pc. neutral voltage transformer
  • 1 pc. neutral grounding resistor
  • 75x92x200 & 100x92x200 cm (WxDxH)

 

Generator Leads Cubicles

 

  • 3 pcs. voltage transformers
  • 3 pcs. current transformers
  • 1 pc. excitation transformer (on request)
  • 3 pcs. surge capacitors (on request)
  • 3 pcs. lightning arrester (on request)
  • 1 pc. voltmeter
  • 75x92x200 cm (WxDxH)

 

 

Dynamic Braking Resistors

 

The speed of three phase asynchronous squirrel-cage motors and three phase synchronous motors is generally controlled by motor drives where frequency of the drive output determines the motor speed, which can be adjusted without dependence on the voltage magnitude.

 

When the motor serves as a generator (rotating at speeds higher than the synchronous speed), the energy generated by the motor increases the voltage in the DC bus of the motor drive. In order to limit this increased voltage to protect the equipment, DC bus voltage must be limited under a critical value.

 

Feeding this energy back to grid is not an economical method due to need of expensive power electronics and control equipments in most cases. Instead, this excess energy is converted into heat through a brake chopper and a braking resistor. Hilkar's external braking resistors provide compact and economical solution for dissipating the excess energy produced by the motor. Our dynamic braking solution is compatible with any duty cycle for various applications with power ratings from a few watts to many megawatts.

 

Advantages

 

  • Manufactured for any power rating and duty cycle
  • Open type or enclosed construction
  • Custom designs are available in addition to standard modules
  • Suitable for any brand and model of Variable Frequency Drives (VFDs)
  • For high continuous powers and areas where space is a limitation, fan cooled braking resistors are also manufactured especially for marine, mining, and traction sectors.

 

Enclosure options:

 

  • Aluminium heat sink enclosed
  • Hot dip galvanized steel enclosed
  • Stainless steel enclosed

 

Remark-1:

 

Ohmic value of resistors for braking purposes should not be less than VFD manufacturers' catalog values. If this minimum catalog value is violated, it can cause equipment damage. If the chosen ohmic value is much larger than inverter catalog's recommended value, braking time gets longer. Braking time is determined by the inertia and speed of rotating parts.

 

Remark-2:

 

If braking time is unknown or close to total cycle time, as a safety tolerance , the resistor continuous watt rating should be chosen the same as the motor's power rating.

 

  • Continuous Power (W): From a few watts to many megawatts
  • Cooling : Natural cooling or forced cooling
  • Protection Degree : IP20 and others

 

Relationship between Over Load Multiplier / Cooling time / Over Load Time can be seen in the following graph.

 

Motor Starting & Control Resistors

 

1. Stator Connected Resistors

 

Motor Starting Resistors are used to reduce the voltage at the motor terminals and also decrease the starting current.

 

Motor Starting Resistors are necessary because the self resistance of a motor armature is very low. When the voltage is first applied, excessive current will flow. Because there will be no back electromotive force (emf) to limit this current, some series resistance can be added to the armature windings.

 

As the motor accelerates, the back emf will build and the current through the resistor will thus decrease. Additionally, the voltage drop on the resistor will reduce, causing the voltage across the terminals increases. With this gradually increasing torque and voltage, the acceleration becomes smooth. The resistance is disconnected when the motor reaches a certain speed. At this point, the motor will run with full line voltage.

 

2. Rotor Connected Resistors

 

Rotor connected resistors are mainly used for motor starting applications which require a high-starting torque, such as loaded belt conveyors in the mining industry. By using external resistors, it is possible to shift the motor maximum (break-down) torque up to a starting torque point for motors under heavy loads during start-up. The resistors are split into steps and controlled via contactors by a motor starting control system. As the motor speed increases, the external rotor resistors are eliminated via shorting contactors until all external resistors are shorted out.

 

Area of Usage

 

  • Overhead cranes
  • Lift trucks
  • Machine tools
  • Conveyors
  • Cement plants
  • Industrial controls
  • Steel mills
  • Ships and submarines
  • On load starting motors

 

Features

 

  • Designed and tested to applicable IEC and IEEE Standards
  • Designed for all squirrel cage and slip-ring induction motors and synchronous motors
  • Durable construction
  • Stainless steel grid or alloy resistance elements
  • High performance in heavily polluted areas

 

Types

 

  • AC Squirrel Cage Induction Motor Resistors
  • AC Slip-ring Induction Motor Resistors
  • Crane control resistors
  • Starting Resistors
  • Speed Control Resistors
  • Synchronous Motor Resistors

 

Selection Details

 

  • Application area
  • Motor rated power
  • Rotor current
  • Rotor voltage
  • Starting Torque
  • Desired starting time (seconds)
  • Duty Cycle
  • Number of starting steps