Dry-Type Transformers
Installation
Location
Factors which should be kept clearly in mind in locating dry-type transformers are accessibility, ventilation, and atmospheric conditions.
Dry-type transformers normally are designed for installation in dry locations. Transformers will operate successfully, while energized, in locations with a high relative humidity. Under such conditions it may be necessary to take precautions that will keep them dry if shut down for appreciable periods of time. Locations with dripping water should be avoided. If this is not possible, suitable protection should be provided to prevent water from entering the transformer case. Precautions should be taken to guard against the accidental entrance of water.
Outdoor installations should be discussed with the manufacturer. Transformers must be protected and placed in an atmosphere appropriate to the design criteria.
Accessibility for maintenance should be taken into account in locating a transformer. Normally this requirement in itself will be sufficient to provide the necessary space for ventilation. Dry-type transformers should be installed in dust and chemical free locations. Locations and atmospheric conditions should be discussed with the manufacturer.
If there is any likelihood that these transformers will be exposed to lightning or severe switching surges, adequate protective measures should be provided.
For installations at high altitudes, reference should be made to the A.S.A. Standards for derating factors, which apply.
Inspection
New transformers should be inspected when received for damage during shipment. Examinations of the unit should be made prior to removal from the transporters vehicle. If there is any visible indication of damage or rough handling a claim should be filed with the carrier at once and the manufacturer notified.
Covers or panels should be removed and internal inspection made for any visible damage to the unit
These inspections should be repeated if units are moved or relocated.
Handling
Appropriate lifting devices should be utilized when moving units. Proper weight capacities should be observed. When handling dry-type transformers outdoors during inclement weather, the units should be thoroughly protected against the entrance rain, snow, or any other foreign matter.
Grounding
The case and core assembly should be permanently and adequately grounded.
Storage
Dry-type transformers should be stored in a warm dry location with a constant temperature. Ventilated openings should be covered to keep out dust. If it is necessary to leave a transformer outdoors, it should be thoroughly protected to prevent moisture and foreign material from entering. When necessary, consideration and absorption of moisture can be prevented or greatly reduced by the installation of space heaters and other small types of heaters.
Safety
Standard safety procedures should be followed when performing any installation or maintenance of transformers. Assurances should be made to de-energize and ground the transformer. It is advised that a qualified individual, well versed in such procedures, perform any installation or maintenance activities.
Dry-Type Transformer Maintenance
Periodic Inspection & Maintenance
Like other electrical equipment, transformers require maintenance from time to time to assure successful operation. Inspection should be made at defined intervals to assure the most satisfactory service from this equipment. Frequency of inspections should be determined by environmental conditions.
Inspections should be made for dirt accumulating on insulating surfaces or for those areas which tend to restrict airflow. Also inspect for loose connections, the condition of tap-changers and the general overall condition of the transformer. Inspections should be made for signs of overheating and voltage creepage over insulating surfaces as evidenced by tracking or carbonization. Evidence of rusting, corrosion and deterioration of the paint should be checked. Corrective measures should be taken where necessary.
Fans, motors, and other auxiliary devices should be inspected and serviced during these inspection periods. The settings of thermal relays should be checked.
Cleaning
If excessive accumulations of dirt are found on the transformer windings or insulators this material should be removed to permit free circulation of air and to guard against the possibility of insulation breakdown. Particular attention should be given to thoroughly cleaning each end of winding assemblies, as well as ventilating ducts.
The windings may be cleaned with a vacuum cleaner, blower, or compressed air. The use of a vacuum cleaner is preferred. The compressed air should be clean, dry and should be applied at a relatively low pressure, (not over 25 psi.). Lead supports, tap-changers, terminal boards, bushings, and other major insulating surfaces should be brushed or wiped with a dry cloth. The use of liquid cleaners is not recommended due to solvents or other corrosive materials which could harm insulating materials. It is recommended that the manufacturer be consulted before any liquid cleaners are used.
Drying of Core & Coil Assembly
If it is necessary to dry out a transformer before installation or after an extended shut down under relatively high humidity conditions, one of the following methods may be used:
- External heat
- Internal heat
- External and internal heat
Of the three methods, the first is the preferred method.
Before applying any of these methods, free moisture should be blown or wiped off of the windings to reduce the time of the drying period.
Drying by External Heat
External heat may be applied to the transformer by one of the following methods:
- By directing heated air into the bottom air inlets of the transformer case.
- By placing the core and coil assembly in a non-flammable box with openings at the top and bottom through which heated air can be circulated.
- By placing the core and coil assembly in a suitably ventilated oven.
It is important that most of the heated air pass through the winding ducts and not around the sides. Good ventilation is essential so condensation will not take place in the transformer or case. A sufficient quantity of air should be used to assure approximately equal inlet and outlet temperatures.
When using either of the first two methods, heat may be obtained by the use of resistance grids or space heaters. These may either be located inside the case box or may be placed outside and the heat blown into the bottom of the case. The core and coil assembly should be carefully protected against direct radiation from the heaters.
Drying by Internal Heat
This method is relatively slow and should not be used if one of the other two methods is available.
The transformer should be located to allow free circulation of air through the coils from the bottom to the top of the case. One winding should be short-circuited, and impedance voltage at normal frequency should be applied to the other winding. At no time should the winding temperature be allowed to exceed 100*C. The end terminals of the windings (and not the taps) must be used in order to circulate current through the entire winding. Proper precaution should be taken to protect the operator from dangerous voltages.
Drying by External and Internal Heat
This is a combination of the two methods previously described. This is the quickest method available.
Use of Insulation Resistance for Determining Drying Time
Drying time depends on the condition of the transformer, size, voltage, amount of moisture absorbed, and the method of drying used.
The measurement of insulation resistance is of value in determining the status of drying. Measurements should be taken before starting the drying process and at two-hour intervals during drying. The initial value, if taken at ordinary temperatures, may be high even though the insulation may not be dry. Because insulation resistance varies inversely with temperature, the transformer temperature should be kept constant during the drying period to obtain comparative readings. As the transformer is heated, the presence of moisture will be evident by the rapid drop in resistance measurement. Following this period, the insulation resistance will generally increase gradually until near the end when it will increase more rapidly. Sometimes it will rise and fall a short range before steadying due to moisture from the interior of the insulation working out through the initially dried portions. A curve with time as abscissa and resistance as ordinate should be plotted and the run should be continued until the resistance levels off and remains relatively constant for three to four hours.
Insulation resistance measurements should be taken for each winding to ground with all windings grounded except the one being tested. Before taking insulation resistance measurements, the current should be interrupted and the winding short circuited and than grounded for at least one minute to drain off any static charge.
Water Systems
Installation
General & Piping
PIPE SIZES ARE NOT TO BE TAKEN FROM SCHEMATIC DRAWINGS OR EQUIPMENT INLET SIZES. The system is to be installed in accordance with the appropriate interconnection schematic diagrams. Adequate planning and layout of the water system must be made prior to installation of the equipment. The total system and component water flow is listed in the instruction manual or on the water schematic.
The following discusses installation requirements. The person responsible for the installation engineering must investigate all federal, state, and local codes to be sure the installation will comply.
When the solenoid activated source to drain emergency water system is used, it will require the dumping of some of the system water. If the system water has been treated to prevent scale, corrosion, or slime, the concentration of pollutants may exceed what is permitted by code to be discharged directly into the plant drain. In this event, the emergency drain water will have to go to a suitable waste treatment.
Non-ferrous piping is always preferred for water-cooled electrical equipment. Rigid copper tubing, type K or type L, and schedule 80 CPVC plastic are recommended. See the Maintenance Section of this manual when using CPVC piping with glycol in the system. Stainless steel is also an excellent choice, but is generally not used because of cost. Where larger pipe sizes are required for the installation, black iron pipe is an economical choice. When black iron pipe is used, it should be properly treated to minimize corrosion. BLACK IRON PIPE IS NOT TO BE USED FOR WATER WHICH IS BELOW 100 MICROMHO/CM CONDUCTIVITY. DO NOT USE ALUMINUM OR GALVANIZED PIPE AND FITTINGS.
A major cause of system startup problems has been pipe dope or Teflon tape getting into strainers. Either type of sealant may be used at threaded joints; however, care should be taken to avoid getting pipe dope or Teflon tape onto the very end threads.
Pipe sizes are not to be taken from schematic drawings or equipment inlet sizes. Pipe sizes should be determined by the installer based on the number of fittings, the length of the run, and the elevations so that the required differential can be achieved at each component. THE TOTAL INTERCONNECTION PIPING PRESSURE DROP MUST NOT EXCEED 10 psi (68 kpa).
Before coupling any of the water-cooled equipment, each component should be thoroughly flushed to remove any contaminants. All interconnecting piping should be flushed just prior to connection. Strainers are to be used for all major system component inlets. Refer to the Maintenance Section for cleaning instructions.
All working parts of the system should be arranged for convenient operation, inspection, lubrication, repair, and ease of maintenance. All piping should be sized in accordance with good industrial piping practice and installed to allow flexibility for expansion and contraction between component parts of the system. Remember, the interconnection piping is to be sized so that the specified pressure differential is available.
If any part of the induction water-cooling system is exposed to temperatures below 32°F (0° C), provisions should be made to insure against water freeze-up. Insulation and/or heat tape should be installed on outdoor piping to the cooler. See the Maintenance Section for winter protection.
Pump Station
The pump station is an integral unit and needs interconnection only. The pump, expansion tank*, air separator, and piping are mounted on a common base which requires a firm, level floor. The station should be installed near the electrical equipment and heat exchanger.
NOTE: Where components are located at extremely high elevations in relationship to the pump station, higher prefill pressure or remote location of the expansion tank to a higher point may be required.
Electrical connections are to be made in accordance with the appropriate electrical diagrams. The size of control wiring is to be a minimum of 14 awg. All wiring is to be selected and supplied by the customer in accordance with accepted engineering practices.
Emergency Water
GENERALLY NOT REQUIRED BY HEATING EQUIPMENT
Two precautions are recommended, either as options by ATM or by the customer. The first measure uses two identical pumps installed in parallel, using one as a standby. The second measure is the provision of a water supply to be used during emergencies. The second measure qualifies as an emergency water supply.
An emergency is defined here as a complete power shut down with either a hot lining, or molten metal in at least one furnace. The water system under these conditions has to carry away the energy lost by conduction through the furnace linings. Since this energy loss is about 10, or 15% of the normal losses, a small turbine, or gas driven pump can be used in parallel with the pump station to provide the necessary water flow. This provides the flow, and keeps the system closed. A water-to-water heat exchanger must also be used to remove the heat from the process water. The sketch shows this in schematic form.
Another way of providing water in an emergency is to supply inlet and outlet solenoid valves with check valves to force the flow in the proper direction. The sketch provided shows this. The short run is nicely cared for by this scheme, but the system is opened to the atmosphere, and recovery from an emergency is painful. Glycol is lost if used, the water is saturated with oxygen, and free air has been introduced to the entire system.
Small low capacity systems can probably justify using the latter method, and maybe even think about using a completely manual valving scheme, but larger systems easily justify the up front expense of the internal pump.
Water Supervision
Note that valves, pressure gauges, and thermometers are to be supplied and installed by the customer unless otherwise specified. Thermometers may be either bulb or bimetallic with a range of about 30° to 240°F (0 to 115 °C).
Pressure gauges should have a range of 0 to 100 psig (0 to 700 kpa) and be installed with gauge cocks. The devices should be readily accessible for maintenance purposes.
Evaporative Heat Exchanger
Refer to manufacturer's instructions for unit location, as they must be located so there is an unimpeded supply of air to all fans. When units are located close to adjoining building walls, discharge air from the unit must be carried above the walls to prevent warm, saturated discharge air from being deflected back to the fan intakes. Note that the heat exchanger's position is ahead of the furnace and other water-cooled components in the water system.
All piping to and away from the unit must be insulated sufficiently to prevent freezing in the piping during cold weather conditions. Heat tapes in critical areas may also be required. See the Maintenance Section for winter protection.
It is most important that an adequate steel supporting structure for mounting be provided for the evaporative heat exchanger. Refer to the manufacturer's instructions for weight loading diagrams, suggested steel supports, holes in frame, and necessary foundation beams. Sufficient clearance must be provided at the end of the unit for tube bundle removal or pan immersion heater removal.
Because rigging procedures vary with each exchanger size, adhere to the manufacturer's specific lifting recommendations. Since most units are broken down for shipment, field assembly of sections is required. Check to make sure the motor shafts are parallel to fan shafts and are in alignment. Check the rotations of the motors and the belt tension. Adjust the float makeup valve to obtain the proper pan water level. The operating water level in the pan is approximately 5 inches (12.7 cm) below the centerline of the overflow connection. Two 3/4 inch pipe fittings have to be located in the cooling outlet water line near the exchanger for installation of temperature controller capillary bulb therm-o-wells (which are supplied with the exchanger). Vents with valves must be supplied and installed by the customer in the supply and return lines of the heat exchanger. These vents will aid in bleeding air when filling the system. Electrical interconnection is shown on the water system control schematic. See the manufacturer's maintenance manual for further information.
Operation of the Water System
System Preparation & Initial Filling
To avoid water system problems it is very important to get off to a good start. A good start-up procedure, like the one given below, can eliminate much of the confusion and frustration associated with water systems.
- The following procedure assumes that the water system is a closed recirculating system. The steps outlined below should be accomplished in a timely manner. It is important that the system not be left open to the atmosphere any longer than absolutely necessary. To do so would negate the beneficial effects of the procedure.
- Fill and flush out the system thoroughly with warm (80° to 120°F) (27° to 50°C) tap water.
- Clean all strainers.
- If no chemical treatment of the water system is planned, proceed to step #7. If the piping or heat exchanger equipment includes ferrous components, chemical treatment of the water to minimize corrosion is strongly recommended.
- Drain the water from the system, then add warm tap water with a solution of either Diversey CL-658 or Calgon CSC-400. Follow manufacturer's directions for use.
- Drain the system and flush it with tap water until water in system is clear and conductivity and pH are similar to tap water.
- Immediately fill the system with water of the quality specified in the "Water Requirements" section of this manual. If chemical treatment is used, the system should be filled with demineralized water of less than 30 micromho conductivity*; followed by sufficient quantity of Diversey CW-4745 low conductivity treatment or Calgon LCS-70 or equivalent to provide 30 to 40 ppm DEHA free residual. Follow manufacturer's recommendations.
For sealed systems, filling of the system is accomplished through a prefill pressure-reducing valve located on the pump suction side. This point is noted on the pump station assembly drawing. Glycol and/or water is introduced at this point with all but the emergency valves open and all the high points of the system vented so that no air pockets are present. When all the air pockets are removed and the system is completely filled with glycol and/or water, close the vents. See the start-up procedure.
An alternate method of filling is a gravity fill. This method must be done at the highest point in the system and may be awkward to perform. For this method, a valve is placed at the highest point in the system and the fill water is poured in at this point.
After checking for proper rotation, the re-circulating pump may be started. When starting the pump, observe the pressure gauge on the pump suction. If this pressure varies when the pump is started, there is still significant air in the system. Caution: Do not continuously operate vertically mounted pumps until all air has been removed from the system. To do so will damage the pump seal. As the pump continues to operate, the air separator will remove the initial air in the system. As this happens the pressure at the pump suction will be reduced so the pump suction is again at approximately 12 psig (83 kpa).* When the pump can be started with little or no variation of the suction pressure, the system is free of air. Final adjustment of the suction pressure will be made by opening the feed valve to the pressure-reducing valve. Once the system is initially filled, the pressure at the equipment should be checked. It may be necessary to adjust the flow on each component in order to obtain the proper differential pressure across each one. The system static pressure will be maintained between 12 psig (83 kpa) and 25 psig (173 kpa) by the interaction of the pressure reducing and pressure relief valves.
Normal Operation
The main functions which must be performed on a daily basis are: checking the suction pressure before and after starting the pump and checking all system temperatures and pressures initially and at operating conditions. Note that the suction pressure will vary between 10 psig (69 kpa) and 25 psig (173 kpa),* depending on the average recirculating water temperature. Low pressures may be reached on very cold days.
Abnormal operation will occur for the following conditions: the water pump will trip off only on electrical power failure, overload on the motor, or high pressure. If the water pump trips off, the emergency water system should be used immediately if there is molten metal in the furnace or hot parts in the coil. The furnaces are protected by differential water pressure switches that will remove power if the pressure differential decreases to less than the design point.
* Will change if pieces of equipment are on different elevations.
The main operations which must be performed are: starting the water pump before applying power to the unit and shutting down the water pump after the furnace has cooled at least a couple of hours after power is off. Exit temperatures of the cooling water should be checked daily. When the unit is running at full power, the exit water temperature must not exceed 155°F (68.3°C) for the coil, transformers, and leads. Capacitor water must be limited to 120°F (48°C) exit temperature.
NOTE: Remember to check temperatures daily for the first week after start-up for future reference. Record water flow and inlet and exit water temperatures whenever practical.
The emergency water system should be visually checked weekly. An emergency system will only work with all hoses connected and no leaks. In the event of hose failure or blow-off, an attempt to replace the hose should be made, or at least maintain some water flow to protect hot coils. The operation of the emergency system should be checked as regularly as practical.
Frequent inspection of all system strainers is required, especially during the first few weeks after initial start-up.
Cooler Operation
Evaporative coolers, when used, are factory preset and require few adjustments. The outlet line from the cooler will have two bulbs installed to control the outlet temperature of the cooler. One bulb will be set to turn on the spray pump about 10°F (5.6 C°) below the required equipment inlet water temperature. The second bulb will be set to turn on the blower motor about 5°F (2.8 C°) below the required equipment inlet temperature. The blower will remain on until the water drops under 5° (2.8 C°) below the required equipment inlet temperature. The spray pump will stay on until the water temperature drops to 10° (5.6 C°) below the required equipment inlet water temperature.
A thermostatically controlled electric heater in the spray water pump turns on at approximately 40°F (4.4 C°) to prevent freeze up in cold weather, and a float operated valve controls the sump water level. After a few days of operation, the float ball may need adjustment in order to maintain the operating level 5 inches (12.7 cm) below the centerline of the overflow connection.
The main recirculating water (being within a closed system) does not evaporate and requires no blow-down to reduce buildup of solids. The sump water is an open system and does require periodic introduction of fresh water. The better the quality of the initial water, the less drainage of sump water is required. Refer to the evaporative cooler instruction manual. The sump drain valve is set to allow enough bleed-off to eliminate scaling the sump.
Maintenance of the Water System
General
When installed properly, only routine maintenance is required on the water system. When started up, the water flow and inlet and exit temperatures of water paths should be recorded and filed for future reference. Daily inspection is required until the equipment has been in continuous service for two months. The maximum outlet water temperature for the induction equipment supplied is 155°F (68.3°C). This temperature will only be realized when the equipment is running at maximum power and when the charge is at the highest temperature for which it was designed. If the system pressure decreases after startup, check all system strainers to be sure they are clean.
After the equipment has been in service for some time, water flows and/or exit water temperatures may vary due to residue buildup in the cooling tubes or line pressure variations. To prevent any of these factors from causing problems, it is important to monitor inlet and exit water and the quality of the water in the system.
The dissolved oxygen, conductivity, pH, hardness, and dissolved solids in the system should be monitored and maintained within the limits as stated earlier in the Water Quality Requirements. Water quality can be maintained by treating the water, or, as an alternative, dumping all or part of the water and making it up with Water that is better than the quality required. Periodic monitoring of pH and conductivity is recommended. These should also be plotted to detect trends in water quality. Equipment is available as an option from ATM for monitoring conductivity.
If system pressures change, the cause is either less pump flow or a gradual buildup of rust and scale in the cooling water piping due to poor water quality. If the cooling water temperature has increased, the cause is usually either a reduction of water flow (due to blockage) or operation of equipment at higher than design power rating.
If the flow of water through the cooling system falls below that required for your equipment and the pump pressure has increased, the probable cause is mineral deposits restricting the effective size of the tubes. This must be corrected immediately since these deposits not only interfere with water movement, but act as insulation which further reduces the efficiency of the coolant. The two types of cooling tube contamination most frequently encountered are mineral deposits and sediment.
SHOULD WATER PATHS BECOME REDUCED OR BLOCKED, EITHER BACK FLUSHING OR CHEMICAL FLUSHING MAY BE USED TO CLEAR THE PATH.
Back Flushing
Back flushing is used as a means of removing sediment from a cooling circuit by reversing the normal flow of water with air pressure. Attach an air line to any convenient connection point near the water supervision equipment on the coil side of the outlet valve of the faulty circuit. Turn the outlet valve off and turn the air on sufficiently to blow the water vigorously backward through the circuit. Remove the air pressure and open the outlet valve. See if the flow has increased and if not, repeat the above process several times. This procedure will usually break up and remove small particles, such as rust, that are interfering with normal water flow but not scale formations. Should the flow remain below normal, chemical flushing should be used.
Chemical Flushing Method
Citric Acid flushing is used to loosen scale, salt deposits, or algae from the water piping. ATM has trained Service Engineers capable of providing this service. The ATM Service Department should be consulted prior to attempting this procedure. The procedure for chemical flushing as used by ATM is as follows:
INITIAL CHECKS
- Conductivity Check (document)
- PH Check (document)
- Indications of freezing water lines
- Inlet Pressure (document)
- Outlet Pressure (document)
- Trace & mark each water path
FLUSHING
- Confirm path (with air if necessary)
- Drain path
- Air Flush Path
- Flush path, note flow (document)
- Flush with fresh water
- Air flush
- Re-connect line to header & component
POST CHECK(s)
- Conductivity check (document)
- PH Check (document)
- Inlet Pressure (document)
- Outlet Pressure (document)
- Check for leaks
- WM1 provided to customer (H2O specification sheet)
Winter Protection
If water-cooled equipment is exposed to freezing conditions, it must be protected. This is accomplished by mixing glycol with the water in the cooling system. Because of the low conductivity requirements with induction equipment, only uninhibited glycols should be used. (Do not use commercial or automotive type antifreezes. These have additives for corrosion protection that are too highly conductive for use in induction equipment. Refer to the section of this manual on water conductivity. Note also that water mixed with pure glycol will have a lower conductivity than the water alone.)
Non-inhibited Ethylene Glycol is used for freeze protection. Typical glycols that are acceptable are:
- Dow Chemical Company Low Conductivity Grade Ethylene Glycol Product Code #30499. (ATM SC# 82260A00)
- Dow Chemical Company Propylene Glycol, Product Code #70511.
These two types of glycol are miscible in each other; there is no problem mixing the two types in the equipment supplied by Ajax. Some compositions of plastic piping, particularly CPVC, may be susceptible to environmental stress cracking when used with higher concentrations of propylene glycol. The piping supplier should be consulted to ensure compatibility.
Please note the precautionary information supplied with glycol. Glycol is flammable, and when it is used precautions must be taken to reduce the risk of fire. The major fire hazard occurs when the solution of glycol and water is sprayed over hot objects. The incidence of this can be almost eliminated if good maintenance procedures are incorporated to ensure hoses don't fail and water paths don't leak for long periods of time without correction.
Typical Concentrations Required to Provide Protection at Various Temperatures
Glycol-water solutions become slushy instead of having sharp freezing points, and are known to provide burst protection to temperatures well below the published freezing temperature. While freezing temperature is dependent only upon fluid characteristics, burst protection is affected by other factors such as provision for volume expansion, piping material, and rate of cooling For most systems however, glycol will provide burst protection to the temperatures shown in the above chart. ATM recommends a mixture of 30% ethylene glycol, which provides burst protection to -40° for most systems. Extremely high levels of concentration are not necessary and are not recommended; at high concentrations, the freezing point actually increases.
Maintenance Schedule
