Datasheet: R5 – Neutral Earthing Resistors (124kb)

Manual: QF3001_01 Installation, Operation & Maintenance Manual for Neutral Earthing Resistors (916kb)

Why use Fortress NER’s?

The Fortress Difference

Fortress has a history of successfully managing large projects and provides value to customers by ensuring we understand the customer’s requirements and expectations. We place an equal importance on technical capability, manufacturing to deadlines, and providing documentation and drawings in a concise and timely manner.

Choice

An extensive range of resistor elements allows selection of the most efficient and cost effective solution for any required duty. Fortress can manufacture NERs with rated times from a few seconds to continuous, any required initial current, and for system voltages up to 66kV.

Predictability

The change in resistance with temperature during operation is small and predictable. This means that protection levels can be predetermined accurately. A Fortress NER will not induce unpredictable phase changes or resonances into the fault current, as may occur with an earthing reactor.

Reliability

NERs may only be called upon to operate a few times in their service life, which may be 25 years or more. Reliability is essential; elements from Fortress have been proven over many years in conditions of severe vibration and extreme climate worldwide.

Features of all Fortress Earthing Resistors include:

• Full compliance with ANSI-IEEE 32, Terminology and Test Procedure for Neutral Grounding Devices
• Stainless steel resistors as standard
• Enclosures ratings from IP00 to IP56
• Type-tested standard designs (certificates available)

Options include:

• Supply of resistor banks only for incorporation into customers’ own enclosures
• Cyclone Wind Loading rated enclosures
• Seismic rated enclosures
• Compliance with AS/NZ 2081.5:2002 Mining Standard for Earth-fault current limiters
• Provision of NER Monitoring at time of manufacture
• Provision of CTs, heaters, special cabling, and other accessories
• Interlocked off-load by-pass isolators
• Single or multiple vacuum contactors or circuit breakers

Enclosure Materials and Design

The standard enclosure material is mill galvanised steel with an epoxy powder coat finish. Alternative materials include both GR304 & GR316 stainless steel.

As standard we offer IP23 enclosures. They keep out birds and vermin and are suitable for outdoor use whilst also allowing good ventilation. We also supply IP33, IP54, and IP55 enclosures. When side mounted cable termination chambers are specified they are IP54 or IP55 as standard.

We routinely supply cyclone wind load rated enclosures to customers in harsh coastal environments and seismic rated enclosures for earthquake prone areas.

Whilst our standard range of enclosures are suitable for most applications we are also happy to provide custom designed equipment if your application requires it.

Additional Switchgear

NERs can be fitted with one or more manual off-load isolators. These can be interlocked if required and can be supplied mounted in the same enclosure as the resistor, a separate compartment, or in a side mounted cable termination chamber.

For medium-voltage power generating schemes which have multiple generating sets, it is often necessary to ensure that only one of the neutrals of the running generating sets is earthed at any time. This can be achieved by fitting the NER with an appropriately rated vacuum contactor controlled from the generating set panel. Fortress can supply contactor rated from 3kV to 24kV fitted in a separate compartment to the resistor.

Fortress has standard designs for the incorporation of circuit breakers with NERs.

Transformer / Resistor Combinations

Fortress can also supply transformer / resistor combinations such as zig zag earthing transformers and single phase earthing transformers as required.

The solution is higher order harmonic filters consisting of capacitors, inductors and resistors tuned to eliminate specific frequencies. The capacitors and inductors allow the fundamental frequency through and divert the harmonics into the filter resistor where the harmonic currents are dissipated as heat and thus lost from the system.

Fortress Systems, often in partnership with Post Glover or other group companies, design, build and test filter resistors in accordance with applicable IEC and IEEE standards to guarantee their performance. With no two installations ever being the same, our experienced engineers develop the proper solution for your particular application and environment. Our low inductance designs are built using all stainless steel elements in corrosion resistant enclosures chosen for your unique specification. Post Glover’s reputation in filter resistors has been built on over 100 years of field performance and independent test facilities, where they have proven their engineering and manufacturing prowess to be second to none.

Design Considerations with Filter Resistors

Power Dissipation

This power is partially stored in the mass of the resistor elements before being transferred to the surrounding environment through convection cooling. Not only is the overall mass of the current carrying material important, but also:

• The surface area of the resistor elements
• The temperature difference between ambient air and the heating elements
• The cumulative effect of the resistors on each other

Resistance Value

The overall filter design dictates the required resistance. As such, it is imperative the Customer specify the nominal value of the resistor as well the desired tolerance.

Additionally, the inherent inductance of the resistor may affect the performance of the filter. Fortress engineers their resistor assemblies to not only minimize this inductance, but also limit the change in resistance as the elements heat up to guarantee a stable operating profile.

Voltage/Insulation class

The resistor must be designed in accordance with local standards (IEEE, IEC, etc.) and consider line to line voltage, arcing distances, creepage distances, BIL withstand level and any expected voltage transients.

Current Rating

The resistive elements, along with the internal and external connections have to be carefully considered and engineered to carry not only the rated current, but also periodic high current transients.

Miscellaneous

Other factors can contribute to the design of the resistor, including physical conditions of the site such as the level of atmospheric pollution, seismic zone, corrosive environment, wind and altitude.

Why use Fortress Filter Resistors?

The Fortress Difference

Fortress has a history of successfully managing large projects and provides value to customers by ensuring we understand the customer’s requirements and expectations. We place an equal importance on technical capability, manufacturing to deadlines, and providing documentation and drawings in a concise and timely manner.

Choice

An extensive range of resistor elements allows selection of the most efficient and cost effective solution for any required duty.

Predictability

The change in resistance with temperature during operation is small and predictable. We use low-inductance resistor elements for easy matching with capacitors and inductors.

Reliability

Filter resistors may operate continuously over their service life, which may be 25 years or more. Reliability is essential; elements from Fortress and Post Glover have been proven over many years in conditions of severe vibration and extreme climate worldwide.

Enclosure Materials and Design

The standard enclosure material is mill galvanised steel with an epoxy powder coat finish. Alternative materials include both GR304 & GR316 stainless steel.

As standard we offer IP23 enclosures. They keep out birds and vermin and are suitable for outdoor use whilst also allowing good ventilation. We routinely supply cyclone wind load rated enclosures to customers in harsh coastal environments and seismic rated enclosures for earthquake prone areas.

Whilst our standard range of enclosures are suitable for most applications we are also happy to provide custom designed equipment if your application requires it.

Such tests are usually carried out against a temporary load bank brought to site for the purpose and removed afterwards, or a fixed dummy load installed with the generator.

Suitcase Load Banks

Fortress suitcase load banks are available in two configurations, allowing for easy travel to out of the way testing locations. This load bank is perfect for transport by one technician due to its lightweight, available casters and telescoping handle. Individual units are useful for loads up to 150kW from the back of a pickup at the jobsite, tight locations or for roof mounted generators accessible only by elevator. Fortress suitcase load banks can be daisy chained together to increase testing capacity.

Available Ratings:

• Max kW (Hand Carry) – 75
• Max kW (Rolling) – 150
• Resolution, kW – 1, 5, 10, 25
• Rated Voltage (L-L) – 240, 415, 480, 690
• Controls – Integral

Stationary Load Banks

Fortress’s line of stationary, outdoor resistive load banks are designed and built to be permanently mounted and used for dedicated, on-site testing. The result of many years of experience, these load banks are built to withstand not only the elements but also continuous duty in difficult conditions. A modular design concept enables larger units to be constructed from standard “building blocks”. This simplifies component sourcing and manufacturing, allowing us to ship your load bank quicker. The resistors elements require no cool-down period between operations; the louvered enclosures are designed for safety and durability.

Available Ratings:

• Max kW – 25 to 1000
• Resolution, kW – 5, 10, 50, 100
• Rated Voltage (L-L) – 240, 415, 480, 690
• Controls – Integral

Portable Load Banks

Fortress’s range of standard portable load banks is designed for testing AC and DC systems, including batteries, uninterruptible power supplies (UPS) and standby generators.

They are available for quick delivery, easily handled by one person, light, robust, simple to use, and reliable.

All units are fan-cooled, which helps to ensure a compact design. The fan supply is taken from the test load itself or from an auxiliary supply of 110 or 230V AC, according to model.

Units are fitted with over temperature protection. To reduce weight enclosures are manufactured from aluminum and fitted with handles and where required have castors to ease maneuverability.

All units can be operated at voltages lower than their nominal rating; power is reduced accordingly.

Available Ratings:

• Max kW – 3 to 500
• Resolution, kW – various
• Rated Voltage (ac L-L) – 110, 240, 415, 480
• Rated Voltage (dc) – 27, 28, 110, 240
• Controls – Integral

Radiator Mounted Load Banks

Fortress offers resistive load banks designed and built for radiator mounting in a variety of configurations and dimensions. Typically sized around 50% of the engine nameplate rating, these permanently mounted load banks eliminate wet-stacking problems and are useful for regularly scheduled testing. Available for use at 240 through 690 volts, the total load and individual steps can be coordinated to suit your particular application. Controls can be mounted on the load bank itself or also available for remote rack mounting for easier access. The standard package includes fusing, master and step controls as well as indicating lamps. Manual control is standard for more than one step, while an automatic feature is an available option.

Available Ratings:

• Max kW – 1000
• Resolution, kW – 5, 20, 25 or 50
• Rated Voltage (L-L) – 240, 415, 480, 690
• Controls – Integral

High Voltage Load Banks

Fortress’s line of stationary, indoor or outdoor high voltage resistive load banks are designed and built to be permanently mounted and used for dedicated, on-site testing. Load banks up to 13.8kV/60Hz and 11kV/50Hz can be supplied either fan forced or naturally ventilated. Using an 11kV load bank directly connected to an 11kV generator or turbine means that a transformer is not required as part of the load bank package and is often a cost efficient method. Ratings up to 20MW are available.

• Wound rotor AC motors with slip ring starting resistors
• Star-delta closed transition starting resistors
• Squirrel cage AC motor resistors
• Crane control systems
• DC series wound motor resistors
• Field discharge resistors

Although AC variable speed drives have, in many cases, replaced these types of motors and control systems, they are often still used on grounds of cost, simplicity and reliability.

Fortress can assist you to replicate existing equipment, even where the original design data is not available and the original equipment manufacturer either no longer exists or no longer manufactures resistors.

Wound Rotor AC Motors with Slip Ring Starting Resistors

The resistor is wired into the motor secondary slip rings, where it dissipates torque energy in the form of heat. It also provides “soft starting” as resistance is removed in steps.

Initial information needed for sizing your resistor:

• Application
• Power
• Secondary volts
• Secondary amps
• Minimum & maximum starting torque
• Start time
• Number of consecutive starts
• Number of equally spaced starts per hour

Star-Delta Closed Transition Starting Resistors

Star-delta is a reduced inrush starting method in which 3 phase motor stator coils are initially connected in a star configuration and switched to delta as the motor’s speed increases. The resistor is in circuit for a very short time during the switchover from star to delta operation.

Initial information needed for sizing your resistor:

• Application
• Power
• Line voltage
• Full load amps
• Duty

Squirrel Cage AC Motor Resistors

Commonly known as a “reduced-voltage” or “ballast” resistor, this resistor acts as a voltage divider for soft starting of the motor.

Initial information needed for sizing your resistor:

• Application
• Power
• Line voltage
• Full load amps
• Duty cycle

DC Series Wound Motor Resistors

The resistor limits torque by limiting current flow to the motor. It is used for starting and stopping the motor.

Initial information needed for sizing your resistor:

• Application
• Power
• Line voltage
• Full load amps
• Starting torque
• Number of speeds
• Duty

For other applications, such as small kW motors, dynamic braking, and field discharge, please give us a call. We offer free engineering assistance to our customers for all motor control applications.

Datasheet: R7 Custom Dynamic Braking (133kb)

When an overhauling or decelerating load on a motor causes the motor to turn faster than the synchronous speed set by a drive, the motor acts as a generator and transforms mechanical energy from the motor shaft into electrical energy. This AC power from the motor flows backward into the drive and causes the DC bus voltage to increase. Unless this regenerative energy is dissipated, once the DC bus voltage reaches a certain value, the drive will trip on bus overvoltage in order to protect itself. Dynamic braking is often the simplest and most cost effective means to dissipate the regenerative energy, thus allowing the drive to safely brake the load.

The rate of braking is dictated by how fast the energy can be put into the resistor, which in turn is determined by the ohmic value of the resistor. Each drive manufacturer specifies a resistance range with a minimum to prevent over current and damage to the drive and a maximum value to give adequate power dissipation capability for the application.

The peak braking current is a function of the drive chopper turn on voltage and the specified ohmic value.

The drive manufacturer normally determines the power rating (watts) needed to prevent overheating during braking duty. When the stop time is short in relation to the total duty cycle we may also need to consider the thermal capacity of the resistor, to ensure that it does not overheat during a single stop. In this case we will also need the absolute time on / time off in seconds.

Initial information needed for sizing your resistor:

• Application
• Peak Power
• Ohmic Value
• Duty Cycle (either a percentage or absolute time on / time off in seconds)

Standard Dynamic Braking Resistors

The Fortress standard range of braking resistors is available on short lead times. The enclosures are made of galvanized steel as standard and are also available in stainless steel. Ingress protection is IP 20 with an option for IP21 and IP23. A terminal box and thermostat are standard.

Custom Dynamic Braking Resistors

Fortress specialise in customer designed dynamic braking resistors for the mining industry. In particular we are able to supply a range of resistors mounted in GR316 stainless steel cyclone rated enclosures that come equipped with an IP56 terminal box including all of the features expected on an Australia mine site. The resistors have been proven on conveyors, stackers, and reclaimers at dry and dusty sites in the Pilbara and in marine environments on shiploaders all around Australia.

If you have a harsh environment or a non-standard requirement, please give us a call.