Cressall Electrical Power ResistorsIndonesia Industrial Parts

OVERVIEW

Cressall manufactures one of the widest ranges of electrical power resistors in the world for applications such as dynamic braking for industrial drives and the traction industry, neutral earthing for MV transformer and generator protection, as well as harmonic filters, motor starters and a range of portable load banks for on-site load testing.

In 2006 Telema SpA purchased a thriving Cressall and since then Cressall has benefitted from being an important part of the world’s leading power resistor group. Benefits that we pass on to our customers. An example is the revolutionary EV2 braking resistor.

Developed by Cressall using new materials and new manufacturing processes, it has reduced the footprint and increased the capacity of dynamic braking resistors and, in the process, opened up new applications for the twenty-first century.

General Information

A much slimmed down Cressall was purchased by the Halma Group in 1990. Halma revived Cressall’s fortunes and in 1993 the company moved to Leicester. New products followed; neutral earthing resistors, portable load banks and standard dynamic braking resistors along with fresh investment in new machinery for mesh expanding, edge winding, wire coiling and a complete sheet metal fabrication plant.

Such was Cressall’s success that they quickly went on to acquire the GEC Rugby, H A Birch and Eaton Cutler-Hammer resistor businesses, extending still further their range of resistor technologies. Incorporating GEC’s edge wound coils and Cutler-Hammer’s traction resistor expertise meant Cressall became by far the most important power resistor manufacturer in the UK.

Cressall Resistors Productss

Cressall Resistors have built an unrivalled reputation for advanced design and manufacturing excellence. Which is why our resistors are used around the world for the most demanding applications.

Neutral earthing resistors for HV, MV and LV electrical systems
Dynamic braking resistors for inverters and motors
Portable load banks for testing batteries, generators and UPS systems
Resistors for renewable energy applications
Electric and hybrid vehicle braking and heating
Load banks for testing diesel generators and gas turbines
Pre-insertion resistors to reduce inrush currents on HV and MV networks
Braking resistors, control resistors and trackside resistors for rail traction applications
High voltage filter resistors used in HVDC, VSC, and within SVC and MSCDN damping networks

Cressall Resistors Products

NEUTRAL EARTHING

NEUTRAL EARTHING RESISTORS (NERS)

Neutral Earthing Resistors (also known as neutral grounding resistors in US influenced regions) are a key component in earth fault protection of medium voltage electricity generation and distribution systems.
Cressall NERs limit the current that would flow through the neutral point of a transformer or generator in the event of an earth fault.

PACKAGED EARTHING TRANSFORMERS & RESISTORS

For delta-connected 3-wire electrical systems with no star point, one solution to the absence of a neutral for connection to the earth or ground connection is to create an artificial neutral by using a zigzag or star open delta earthing transformer with a low voltage secondary winding. The zig-zag neutral or the transformer secondary can be connected to a suitably rated resistor to limit the fault current.
The Neutral earthing transformer (NET) will be a dry type, rated for the on time of the earthing package. This may be a short term rating of 10 or 30 seconds, or in some cases continuous – for example for offshore installations where safety considerations may require that faults are not cleared immediately.
Cressall Resistors manufactures complete earthing transformer systems of this type, with the transformer and resistor mounted in a single enclosure.

GENERATOR EARTH SYSTEMS

The increasing demands for electricity and the prohibitive cost of installing transmission lines (along remote, inaccessible or uneconomical routes) means stand-alone and emergency generators are being installed in challenging locations.
To support this requirement Cressall introduced their modular range of neutral earthing resistors with standard cabinet designs to house 1, 2, 3, 6 and 9 contactors, for generators from 3.3 to 13.8kV system voltages.
It is important to remember that with medium-voltage power generating schemes that have multiple diesel generating sets, it is necessary to ensure that only one of the neutrals of the running generating sets is earthed at any time (this is to avoid the possibility of currents circulating through multiple connected neutrals).

NER STANDARDS

The only industry standard specifically covering Neutral Earthing Resistors is IEEE C57.32a (2020) “Standard for Requirements, Terminology, and Test Procedures for Neutral Grounding Devices”.
For applications outside of the of the USA, Cressall adopts the IEEE-C57.32a (2020) standard except for insulation coordination where IEC60071 is applied.
There is currently no IEC standard specifically for NERs. However, IEC 60076-25 which is specifically for NERs is currently under development. This standard is expected to be issued soon.

NER DESIGN & CONSTRUCTION

The resistance alloys used are high temperature stainless steels capable of withstanding temperature excursions to 1000°C whilst retaining their strength.
NERs designed for operation to higher temperatures require less active mass, resulting in more compact and economical designs.
All the stainless steels used to make earthing resistors elements increase in resistance as they get hotter, the new industry standard (IEEE C57.32a) limits this resistance change to <67% over the temperature range of the resistor. This may not always be appropriate depending on the application and protection scheme employed. Cressall can offer alloys compliant with C57.32a (2020) as well as alternative lower cost solutions if permissible.

LOAD BANKS

Power prove is a new load bank division from cressall resistor. Our dedicated load bank division offers you:

An extended load bank product range
Competitive lead times and pricing
Enhanced features; power measurement, data logging, remote control and multi-load bank networking
Comprehensive support and product documentation

Load bank applications

Load banks are used in a wide range of industries and critical infrastructure such as Healthcare, IT, finance, production plant and temporary events. The role of load banks in these applications include:

Generator performance testing & maintenance conditioning
Battery discharge testing
Load interruption protection – ballast

Model Load bank Product

AC Model

6kW AC6
30kW AC30
100kW AC100
200kW AC200
300kW AC300
500kW AC500
1350kW AC1350

DC Model

70A DC70
110A DC110
210A DC220
600A DC600

Dual AC & DC Model : 30kW Dual 30

DYNAMIC BRAKING

NEUTRAL EARTHING RESISTORS (NERS)

Cressall manufactures DBRs for any application, with power ratings from a few watts up to many megawatts and with any duty cycle.

Suitable for any power rating and duty cycle
Suitable for any make of drive
Standard or custom designed
Compact and economical standard range
Complete enclosed solutions or open assemblies for installation flexibility

STANDARD BRAKING RESISTORS ON DEMAND

Cressall’s standard ranges of high capacity dynamic braking resistors (DBRs) for regenerative braking are low cost, easy to specify, quick to install and with ratings to suit inverter drives of any power. Our wide range of resistor technologies means that we can select the most technically appropriate and cost-effective resistor design for any application, whether continuous, intermittent or infrequent. We offer two product ranges to cover continuous powers up to 100kW:

ES and DBR ranges for powers to 25kW
Expanded mesh and HPR Grid ranges for powers to 100kW

CALCULATING BRAKE RESISTOR SIZES

A drive motor can also act as a generator. If the drive system is built so as to allow reverse power to flow then this power can be fed into a resistor, thus taking kinetic energy out of the system and causing whatever is driving the motor to slow down.

The rate of braking is determined by how fast the energy is absorbed into the braking resistor. The DC link capacitance of any inverter drive can itself absorb 3-5% of the regenerated power. For non-critical applications these losses, together with the mechanical losses in the drive system, may provide enough braking. Higher powers, up to 100% or more of the motor’s full load torque rating, can be absorbed and then dissipated by a braking resistor connected across the DC bus. Where the braking power is only a few tens or hundreds of watts a resistor mounted internally to the drive itself

The braking resistor is switched on by a separate control unit, activated by a sensor which is monitoring the voltage level of the DC bus and switching on the braking resistor when this voltage rises above some pre-set trigger level as a result of the reverse power flowing into the drive. There may be temperature sensing in the braking resistor to prevent overloading of the drive. All the energy is used in heating the resistor; some is dissipated during braking, the rest after the stop while the resistor cools. This is why we must know the characteristics of the duty cycle before we can specify the right size for the braking resistor.

EV ADVANCED RESISTORS

Manufactured from advanced materials the EVT and EV2 have a patented design that encapsulates and totally separates the resistor elements from the water based coolant providing a modular, light weight, low volume, high power solution for water cooled applications.

Typically the EV range are 10% of the volume and 15% of the weight of the equivalent conventional convection cooled DBR. Units can be combined together to handle from 10’s to 100’s of kW and supplied as individual components, frame mounted assemblies for integration in customer’s systems or completely enclosed multi-banked systems that include inlet/outlet manifolds, flow and temperature monitoring.

PRE INSERTION RESISTORS

A PIR is a far simpler device which requires a far less precise control system offering long term reliable system operation in all environments.

Resistors are designed based on the system voltage and the energy of the switching transient.

Cressall have supplied resistors for pre-insertion applications including on shore and off shore wind farms, high voltage DC (HVDC-VSC) installations and industrial generation sites, we can supply resistors for any voltage and energy rating and as fully enclosed units or open resistors for installation in customers’ equipment.

SURGE SUPPRESSORS

Cressall can now offer ZORC™ products, a range of unique high-frequency transient overvoltage surge suppressors for the protection of motors, transformers, generators and filter banks from steep wave-front, short rise-time, high magnitude, spikes, surges and other transient voltages, generated by switching and certain other sources.

Features:

Saves money by eliminating production downtime due to insulation failure.
Protects motors, generators and transformers throughout their service life.
Eliminates multiple pre and re-strike transients associated when switching on or off with vacuum and other switchgear types.
Standard and intrinsically safe models available.
Three and single phase

HV FILTERS

The demand for higher power quality and better network efficiency has led to the increasing use of static VAR compensators (SVC’s) and mechanically switched capacitor damping networks (MSCDN’s) in high-voltage three phase distribution networks throughout the world.

Harmonic filters are designed to allow through currents at the specified frequencies and to divert unwanted harmonic currents into the resistor, where they are dissipated as heat in a safe, controlled and reliable way and so removed from the system.