RESISTANCE BOXES

Product Description :
o The resistance boxes are designed for both ac and dc applications with uses in winches, E.O.T Cranes, Rolling mills, Steel plants, Flour mills, Cement plants, Power plants, Coal mines, etc, for speed controlling and developing higher starting torque. Our resistance boxes are designed as per BSS/VDE/NEMA/IEEE standards and can also design and manufacture resistance boxes as per standards specified by the customer. The resistor grids are either made of stainless steel wire or punched steel sheet, making these resistance boxes are suitable for a maximum temperature rise of 375°c as stipulated in BSS specifications. In case of S.S grid resistance boxes, the resistor grids consist of corrosion resistant SS wires or strips. The current rating generally ranges from 7 amps continuous to upwards and selection of the size of the wire is based on the technical data of the motor on which the resistance box is to be connected. Higher ratings are also possible by using multiple parallel paths, where as in case of punched steel resistors, the grids are made from nickel chromium alloy sheet steel. Depending on the rating required, the grids, which were previously punched on a die punch are assembled to form the desired resistance box. The inherent strengths of the steel itself is quite high and owing to the reinforced and pressed construction, the rigidity of the punched grids is even higher and since the grids are in the form of punched sheets, they are completely immune to shock and vibration.

Edge wound Resistors are designed and built to meet the most demanding mechanical and electrical requirements in the industry. They are made from continuous strip of non corrodible chrome alluminium steel alloy, wound on its edge to form a elliptical / circular helical resistive element. The element is then mounted on solid porcelain insulators over one piece of M.S / S.S pressing called center support. Stainless steel Welded terminals at both ends of the resistor provide the means of connection and terminations. This is a typical and most wanted design as on today.

RESISTANCE BOXES

SALIENT FEATURES
Well ventilated lowered enclosures on sides along the length, and load bearing members along the depth of adequate strength for free standing and top canopy for protection from rain.
Enclosure protection conforming to IP-00, IP11, IP-23, IP-33, and IP-42 or totally enclosed IP-54 are constructed as per customers requirements.

Resistor elements are made from unbreakable , joint less & rust less material like :

o Stainless Wire formed Grid (AISI 304) typr ' WRS '
o Stainless Steel Wire (AISI 304) wound on porcelain Insulators mounted over Steel Plate as center strip.
o Punched Stainless Steel Plate type Grid (AISI - 304) type 'PRS'.
o Punched Stainless Steel Plate type Grid(AISI 406 - Fechral ) type 'FRS'.
o Edge wound Fechral Strips in elliptical & circular shape on porcelain Insulators mounted over Steel Plate as center strip.

All terminal are located at the bottom and are clearly marked with printed name plates to facilitate easy identification and wiring. Each junction point is well insulated from the other by means of mica tubes and mica washers.

The Resistors are designed to meet both Indian as well as International Standards such as IS:1822-1967, IEEE-32. BS:587 and VDE.

STAINLESS STEEL WIRE FORMED GRID RESISTANCE BOX TYPE : 'WRS'

Resistors type 'WRS' are manufactured from Stainless Steel (AISI 304) having temperature co-efficient of 0.094% per deg C, wire formed grids, making them rust less , unbreakable and light in weight. there is provision at each grid to have a tapping, so that resistance value between steps could be altered. These Grids are generally used for Rotor Current of maximum 54 Amps for 10 minutes and 42 Amps for continuous duty. As for Rotor Currents that are higher than these values, two or three grids will have to be used in parallel. These Resistors are designed and manufactured to meet different classes of service in various industries such as, E.O.T. Cranes, Flour Mills, Conveyors, Elevators , Rope Haulages, Winches, Rubber Mixing Mills, Coke Oven Machines etc. for developing starting torque or for speed control.

WIRE WOUND RESISTANCE BOX TYPE : 'WRS'

Resistors type 'WW' are manufactured with Stainless Steel Wire(AISI 304) having temperature co-efficient of 0.094% per deg. C wound on Steel Plate with Porcelain Channels at the edges. These Resistors are widely used for Higher Resistance values, but, lower Current, e.g. as Economy Resistors have provision for termination on any plate.

PUNCHED STAINLESS STEEL GRID RESISTANCE BOX TYPE:'PRS'

Resistors type 'PS' are manufactured with grids punched out from Stainless Steel Plate (AISI 304). Each Resistor Grid has provision for termination which helps in changing the step Resistance Value of a given Resistor Assembly without dismantling the whole assembly. These grid retain the end of the Grids and steel remain cool which eleminates hot spots from developing. These Resistors are ideally suitable for higher currents are being patronised for heavy duty service for use in Steel Mills, Coal Mines, Foundries, Forklift Trucks, Dynamic Breaking resistors, etc and those applications where the electrical equipment may be subjected to severe vibrations.

PUNCHED FECHRAL GRID RESISTANCE BOX TYPE : 'FRS'

Resistors type 'FRS' are manufactured with grids punched out form Plates of Steel - Chromium - Alluminium alloy (widely known as 'Fe Cr Al).

CAST IRON RESISTORS TYPE : 'CIR'

Cast iron Grid type Resistor has now become obsolete and it is not in use widely by Crane manufacturers and Steel Plants abroad and in the country due to various disadvantages. But we can give 1 :1 replacement to our any of the customer as a special case.

GENERAL CONSTRUCTION FEATURES FOR ALL RESISTORS AND ASSEMBLIES

Degree of Protection is IP -33 Unless otherwise specified however any degree of protection IP - 00 to IP - 55 can be offered. Tested designs are IP - 55, IP - 33 and IP - 43 .

Canopy is sloped to prevent accumulation of water.

Overhang is provided on request to cover terminal box.

Gl Wire Mesh below canopy is provided for ventilation purpose. This feature does not exit for IP - 55 enclosures

Basic construction of enclosure is an angle iron welded structure which provides rigidity.

Removable bolted side covers of 1.6 to 2 mm thick mild steel are louvered for ventilation from all the four sides. No louvers are given for IP 55 enclosures

GI wire mesh is welded from inside to assure required degree of protection..

Hinged doors are provided whenever any instruments like relays or meters are to be flush mounted.

Forged Eye Bolts or Lifting Angles ensure easy handling.

PAINTING

Then enclosures are painted with synthetic enamel paint of specified shade.

Other options are epoxy paint or aluminimum paint.

Pretreatment which includes degreasing rust / scale removing, phosphating as per applicable standards is done followed by 2 coats of finishing paint of required shade.

Oven drying or stoving is done on request.

INTERNAL FEATURES OF RESISTOR ENCLOSURES

Resistance banks are bolted on angles welded to the angle iron structure, facilitating easy draw out facility when required.

The Grids are supported on electro plated steel rods insulated with High quality Mica Tubes. Insulation between grids to grids is given by means of Mica Washers.

The tie rod is insulated from the supporting structure by 3 Groove Insulators.

In case of continuous current ratings for better heat dissipation, perforated sheet with welded GI wire mesh is provided at the bottom.

Foundation channels welded to the angle iron structure are provided on two sides with arrangement to fix on foundation by bolts

Gland plate for bottom cable entry in terminal box is provided if applicable. In case of bus duct connections, a flange of specified dimensions is provided for connection to transformer.

Terminals are brought through porcelain bushings of appropriate voltage class.
In case of higher voltage the banks are placed on stand off insulators housed inside the enclosures.

Optional features cab be Provided on request :
# Safety Screen for enclosures
# Stand off insulators
# Supporting structures
# Aluminium covers instead of MS.
# Hot dip galvanised enclosure
# Stainless steel hardware

DESIGN OF RESISTOR ELEMENT

Resistor elements are designed to carry rated current for the rated time without exceeding specified temperature limits. In case of short time ratings, dissipation is negligible and the temperature rise for the resistor element depends on its capacity to store the energy generated in proportion to the mass and specific heat of the material used.
When the current flows continuously for a relatively long duration, the temperature of resistor element increases and then stabalies at value for which energy supplied is entirely dissipated to the atmosphere. Hence such resistors are designed to allow for maximum heat dissipation.

TEMPERATURE RISE LIMIT

Unless, otherwise specifically confirmed by us, all the resistors, are designed for Temperature Rise up to 375 deg. C. over ambient temperature ,except Dynamic Breaking Resistors . Further resistors can also be designed as per customers requirement & specifications for different temperature Rise limits and for that matter any limit can be achieved. Dynamic Breaking Resistors are designed for maximum Temperature Rise of 760 deg. C as per IEEE 32.

MANUFACTURER'S TOLERANCE

The total Resistance values and the Step Resistance Values will be within a tolerance of +/- 10% of the specified value.

TESTS CONDUCTED AT OUR WORKS

Following tests are conducted by us or jointly with the customers representative at our Works before dispatch:
" Visual inspection for general workmanship, quality and finish.
" Dimensions as per Drawing.
" Resistance values measurements for total resistance per phase and step resistance values.
" Measurement of Insulation Resistance by Insulation Tester.
" High Voltage Test at - 2 KV to 4.5 KV for 1 Minute between live resistor and earth point.
" Temperature rise test is done at rated current for continuous duty subjected to maximum temperature rise should not be more than 375 deg c over ambient temperature or as per customer's specifications.

DATA REQUIRED FROM CUSTOMER FOR OFFERING RESISTOR ASSEMBLY

The following basic data is required for submitting an offer and subsequently supply the unit if the order is placed on us:

HP/KW of the Motor.

Rotor Voltage of the Motor (RV)

Rotor Current of the Motor (RA)

Duty cycle of the Motor (25%, 40%, 60% OR 100% CDF)

Type of Controller (Master Controller or Push Button or Drum Controller) and its No. of Steps used to cut the resistance.

Type of Resistor Grid Element required (WRS, PRS , FRS or CIR)

Type of Enclosure Protection required - IP-23, IP-33, IP-42 or IP-54)

Temperature rise limit.

Space available for the resistance box.

MATERIAL STURDINESS RESISTIVITY MICRO OHM / CM CORROSION RESISTANCE COST SCALE 1 TO 5 FREQUENT APPLICATION AREA CAST IRON CAST STAINLESS BRITTLE STURDY 72 72 FAIR GOOD 2 4 GROUNDING STARING LOADING DAMPING PUNCHED STAINLESS STEEL STURDY 72 GOOD 3 LOCOMOTIVES STARTING GROUNDING ROD / WIRE FORMED STAINLESS STEEL STURDY 72 GOOD 3 GROUNDING LOCOMOTIVES STARTING EDGE WOUND STAINLESS STEEL STURDY 72 GOOD 4 STARTING WIRE WOUND STAINLESS STEEL CONSTANT NICHROME MANGANIN KANTHAL STURDY 72 49 123 43 123 GOOD 3 4 4 3 4 LOADING STARTING DAMPING EDG WOUND CHROMEALUMINIUM ALLOY (AISI 406) FRAGILE 123 FAIR 5 LOCO MOTIVES STARTING PUNCHED CHROME ALUMINIUM ALLOY (AISI 406) STURDY 123 FAIR 4 GROUNDING STARTING

DATA TO ACCOMPANY THE ENQUIRY

The following data is required to be sent along with the enquiry : o Material of resistor o Time Rating o Current Rating o Sheet Thickness o Outdoor / Indoor Sheet o Rotor Voltage o Slip o No. of steps o Temperature rise o Voltage Class o Ohmic Value o Protection Class of enclosure o For starting resistors o Rotor Amps o Starting & Full Load Torque o Type of Coating (Synthetic Enamel Paint / Epoxmy paint / Hot dip Galvanised)

OPTIONAL FEATURES

o Space Heater with Thermostat o Aluminium Covers instead of MS o Supporting Structure Safety Screen o Earth Fault Relay o Cable Sealing kit o Glands o Non Magnetic Gland Plate o Stand off Insulator o Earth Fault Current Transformer o Ammeter o Off Load Isolator / On Load Isolator o Lugs o Indicating Lamps