1-Ph Padmount Manual

INTRODUCTION

This instruction manual provides general information for the installation, operation, and maintenance of the Maddox single-phase padmount transformers. These units are designed for outdoor installation on flat, level pads or foundations. All high- and low-voltage cables are installed through an opening in the pad beneath the cable termination compartment. The compartment is designed for padlocking and has barriers to resist tampering and vandalism.

RECEIVING AND INSPECTION

Maddox padmount transformers are shipped filled with insulating transformer oil. Immediately upon receipt, and before being put into service, transformers should be carefully inspected for any external damage or loose parts caused by shipping or handling. Note any damage presumed to have occurred during shipment, and contact your Maddox sales representative contacted.

Each unit has been carefully assembled and inspected at the factory. Extreme care is taken in the processing and sealing of the transformer to ensure that it is clean and dry, and of adequate dielectric strength. Therefore, it is not recommended that the transformer seals be broken. If it is decided, however, that the transformer is opened, adequate precautions should be taken as outlined elsewhere in these instructions.

HANDLING AND INSTALLATION

(Caution: Do not lift double-stacked transformers by the lifting provision. A forklift truck must be used for handling by means of bottom transformer pallet.)

Transformers should be lifted by the lifting provisions only. The bolts used for banding the unit to the pallet may be used for lifting. Do not use longer bolts for lifting. The transformers must never be moved or lifted by means other than the lifting provisions provided for that purpose.

When moving a transformer on a pallet with a forklift, the forklift should be of proper capacity. Forks should be of sufficient length to extend completely through the shipping pallet. Transformers should be lifted with the tank (the compartment that contains the core/coil assembly and transformer insulating fluid) facing toward the forklift truck. It is not recommended to lift transformers with the door or the hood facing the forklift truck as it is not safe and may cause the transformer to tip and fall. Lifting an un-palletized transformer with a forklift truck may cause damage to the finish of the unit.

Do not use jacks or tackles under radiator panels if supplied. The units may be skidded in both directions. With the sill and door in place, the unit may be rolled in both directions using rolling bars. The sill of the cable compartment may be unbolted and removed. The compartment door may be removed after first bending the spring-action hinge stop. For best operation and assurance of proper electrical insulation to ground, the transformer should always be installed and maintained on a flat, level surface while energized. The transformer pad interface should not have gaps that could defeat the tamper resistance of the transformer.

Ensure that all hardware removed during installation is securely replaced in order to eliminate any openings into the cabinet or any other potentially energized area of the transformer. Check to make sure that any protective barriers are securely in place, the cabinet is completely closed, and locking provisions are installed before leaving the transformer site unattended. Maddox takes no responsibility for damages due to improper installation. The customer is solely responsible for completing all installation work in a good workmanship manner and within industry standards.

OIL

Transformers are thoroughly dried at the factory and filled with mineral oil having the minimum dielectric strength of 30 kV at 60 Hz when tested per ASTM D-877. This Mineral oil contains <2 ppm of PCBs at the time of manufacture. The transformer should never be energized unless it is filled with oil. If it should be found necessary to add to or replace the oil in the transformer, use only clean, dry oil having a minimum dielectric strength of 30 kV and <2 ppm PCBs. Before opening the transformer, sufficient time should be allowed for the transformer to come to temperature equilibrium with the air in the room to eliminate the possibility of moisture condensation from the air.

The natural rubber hose should not be used in the transfer of oil.

CONNECTIONS

Refer to the transformer nameplate for the kVA rating and the permissible connections. No connections other than those shown on the nameplate should be made. None of the connections should be changed while voltage is applied to the transformer.

For three-wire low-voltage connections, the loads between the line terminals and neutral should be as nearly equal as possible. More than one-half of the rated kVA should not be applied between any one-line terminal and neutral.

Provisions are made for grounding the tank by means of tapped pads and ground connectors.

GROUNDED-WYE TRANSFORMERS

Padmount transformers normally have one end of the high-voltage winding brought out through insulated bushings and the other end of the winding connected internally to the tank. A substantial and thoroughly reliable ground connection should be made between the tank and low resistance ground through a conductor of adequate cross section. One or more external grounding pads are provided in the tank at the front of the unit. It is imperative that both the tank and the low voltage neutral be solidly and permanently grounded to the common neutral of the system before the transformer is energized. If this is not done, a high voltage may be impressed between the low voltage circuit and ground constituting a hazard to life and property. The safest procedure is to first make the ground connections, then the low voltage lines, and finally the high voltage connections. When the transformer is removed from service, all high-voltage connections (including those to protective devices) should be opened first.

PRIMARY TERMINATIONS

Primary terminations are made with shielded separable insulated cable elbow connectors, used with externally clamped bushing wells. Loadbreak or non-loadbreak bushing inserts should be used with the wells unless integrated bushings are furnished.

Bushings are provided with tabs to accept a bail, used as a positive hold down for elbows. The bail prevents accidental removal of elbow connectors under energized conditions.

When removing cables from the bushings, they may be easily transferred to an adjacent parking stand. The parking stands will accept open plug-type accessories available for loop feed, grounding or insulating the terminators during troubleshooting, sectionalizing, or maintenance. On transformers equipped with bushing wells, the bushing inserts may be changed or replaced at the installation site.

Changing inserts does not affect the transformer seal.

SECONDARY TERMINATIONS

Stud-type externally clamped bushings are used as standard. Spade terminations are available upon request. The neutral terminal consists of an insulated bushing with a ground strap connecting the bushing to ground. To avoid damaging the bushing when blade types spades are added, replaced or interchanged, first hand tighten the jam nut on the stud. Second, install the spade and back the jam nut against the spade with a wrench, locking the nut and spade together on the stud.

OVERLOAD AND OVER VOLTAGE PROTECTION

Transformer protection against overloads and over voltages may be obtained by having the unit supplied with suitable devices from the factory.

A. Bayonet Fuses

Maddox transformers may be equipped with a bayonet-type expulsion fuse. The externally operable bayonet fuse assembly provides load break capacity by simple hot stick withdrawal. Transformers incorporating this device must not be applied to primary distribution systems where the available fault current will exceed the maximum current interrupting capability of the bayonet fuse. Where the available fault current does exceed the maximum current interrupting capability of the fuse, current-limiting fuses should be used.

The fuse operates as follows:

1. Vent transformer by opening the pressure relief device with hot stick. Next, standing to one side of the transformer, attach hot stick to fuse holder eye and twist hot stick to unlock fuse holder.
2. Turn fuse holder 90° in tube to break the seal between the seal gasket and the outer tube assembly. NOTE: If tank pressure is not released, fuse holder may be forced out of transformer. Maintain control of fuse holder at all times.
3. Draw the fuse holder out quickly 4 to 6 inches to interrupt the load. Wait a few moments for the oil to drain into the tank.
4. Remove fuse holder from outer tube assembly and wipe off fuse cartridge holder and fuse cartridge.
5. Use a wrench to remove the fuse cartridge from the cartridge holder.
6. Remove end plug from fuse cartridge using two wrenches. Use screwdriver or other tool to straighten the tulip tip end of fuse element and push fuse element out of fuse cartridge. NOTE: Replace fuse cartridge if damaged.
7. Insert replacement fuse element into cartridge from either end. Tulip tip may have to be closed slightly to allow insertion into cartridge.
8. Install the cartridge and fuse to the holder with the formed end ferrule towards the holder. Secure the holder while using a wrench on the flat of the cartridge ferrule and torque to 50-70 in-lbs.
9. Spread tulip tips of fuse before installing end plug. Tighten end plug to expand the tulip tips using a wrench on end plug while holding fuse cartridge with wrench on flat of ferrule next to end plug and torque to 50-70 in-lbs.
10. Remove end plug and inspect the tulip tips to see that they are uniformly expanded to insure even contact. Replace the end plug and torque to 50-70 in-lbs.
11. Check oil level at oil fill plug, and add oil if necessary.
12. Attach end of fuse holder assembly to hot stick and insert holder assembly firmly into the outer tube assembly. Twist the locking handle so that the latch engages the outer tube shoulder. NOTE: Visually inspect the inner fuse holder assembly to ensure it is installed properly.
    WARNING: The bayonet fuse is not recommended for fault closing. Serious personal injury may result if attempted. Internal fault conditions can cause the transformer to rupture. Always energize transformer from remote location to be safe. This device was designed and intended for under oil application only. Refer to Step 11 for correct oil level.
    CAUTION: Do not re-energize suspected failed transformer. When replacing a blown fuse, the feed circuit should be opened and closed from a remote location. After fuse replacement, the bayonet should be replaced using the procedure described above and re-energized from a remote location. If equipment is re-fused while energized, the fuse could close in on the system's maximum fault current. Any equipment that has a suspected failure should not be closed in with this fuse. The bayonet fuse is designed to be operated in accordance with normal safe operating procedures. These instructions are not intended to supersede or replace existing safety and operating procedures. The bayonet fuse should be installed and serviced only by personnel familiar with good safety practices and the handling of high-voltage electrical equipment.

B. Internal Expulsion Fuses

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Some Maddox transformers may be equipped with internal expulsion fuses that cannot be replaced. The fuse is in series with the HV winding, and in case of internal failure of the transformer or overload, the protective link disconnects the transformer from the line without affecting line fuses or breakers.

Internal expulsion fuses should not be used on primary distribution systems where the available fault current exceeds the maximum current interrupting capability of the fuse element. Where the available fault current does exceed the maximum current interrupting capability of the fuse, current-limiting fuses should be used.

C. Internal Current Liming Fuse

Maddox transformers are also available with internal current limiting fuses that will limit the energy let through into the fault.

D. Lightning Arresters

Elbow type lightning arresters may be applied to Maddox transformers by the end user.

E. Secondary Breakers

Some Maddox transformers are protected against secondary overloads and short circuits by an internally-mounted circuit breaker. The function of the breaker is to open the low-voltage circuit and protect the transformer from faults or severe overloads.

The breaker operating mechanism is designed to be operated by a lineman's hot stick. Transformers are shipped with the circuit breaker in the closed position.

To open the breaker manually, move the handle fully counterclockwise so that the pointer moves from the "C" (closed) to "O" (open), at which point the circuit is open. Verify that the circuit breaker is latched in the "open" position. To ensure the discharge of the static charge, which is sometimes present in the low-voltage winding due to capacitance, it is recommended that the low voltage be grounded after opening the circuit breaker until after the high voltage is disconnected.

To close the breaker, rotate the handle fully counterclockwise to "R" (reset), which engages the latch mechanism, and then clockwise to "C" (closed). If a fault or an excessive load exists at the time the breaker is closed, the breaker will reopen even though the handle is held in the "C" (closed) position.

Some circuit breakers are equipped with an emergency overload device that can be used to restore service following a circuit breaker operation due to overload. The emergency overload lever is located immediately above the breaker operating handle. With the emergency lever in the normal position, the breaker will trip at its normal setting as calibrated at the factory. Moving the lever in a clockwise direction increases the setting, so a higher temperature is required to trip the breaker. The emergency setting may be adjusted to an intermediate or extreme value. This emergency setting provides extra load capacity and still permits manual breaker operation, and also retains short circuit protection of the transformer. It is important that the emergency setting be used only when, and as long as, absolutely necessary because its use will result in a reduction of transformer life.

A meter seal is provided on the emergency lever to prevent tampering. It is recommended that a new seal be installed on the lever when it is returned to the normal position after emergency operation.

The breaker is a thermal and short-circuit protective device for the transformer. It is not recommended that the breaker be used for routine disconnect operations.

F. Internal Fault Detector

Some transformers are supplied with an Internal Fault Detector (IFD). The IFD is a mechanical sensor that activates when sudden pressure from internal arcing occurs inside the transformer, releasing a visible non-resettable orange indicator alerting crews that the transformer is faulted. The IFD also incorporates a standard pressure relief valve.

The orange shipping lock on the IFD should be removed after the transformer is installed and before it is placed in service. The shipping lock should be re-installed if the transformer must be relocated to prevent accidental operation of the IFD.

SWITCHING DEVICES

Dual Voltage and Taps:

Maddox transformers rated for more than one primary voltage are equipped with a dual voltage switch and/or tap changer. These switches are externally operated but should never be operated while the transformer is energized. When switching from one voltage to another, make sure the switch is in the proper position before reenergizing the transformer. After turning the switch, tighten the locking device to minimize the possibility of unintentional movement. Units equipped with dual voltage and tap changer switches should be operated with extreme caution. Taps should only be changed when a dual voltage switch is set in the series (higher) voltage position, otherwise, serious damage to the transformer could result.

Internal Loadbreak Switches:

Internal loadbreak switches may be supplied with the transformer. These switches are designed to interrupt rated current only, and they are not designed to interrupt fault currents. Consult the labels on the transformer front plate near the switch for instructions on operating the switch.

GASKETS

Bushing gaskets are all made of Buna-N Nitrile rubber. Gaskets may be reused if not damaged.

STORAGE

Transformers should be stored filled with oil and in a clean, dry place. If possible, they should be stored where there are no extreme temperature changes. Before the transformer is put in service, it should be checked in the same manner as when received.

MAINTENANCE

A periodic visual inspection of the transformer is recommended. At such times, the general condition of the following should be noted:

1. High voltage bushings

2. Low voltage bushings

3. Arresters (if provided)

4. Enclosure integrity (hinges, locking provisions, corrosion, etc.) 

5. Evidence of oil leakage

6. Ground connections

7. Accessories

8. Safety labels 

9. Transformer tilt.

Where tanks show evidence of rusting or deterioration of the finish, they may be cleaned and then retouched with paint. Remove all loose paint and rust by wire brushing, scraping, or sanding. Clean the surface using a good solvent. Apply an acrylic lacquer, alkyd enamel, two-part urethane, or a silicone alkyd primer, allow to dry, and then apply a color-matched, compatible top coat and allow to dry. If metal is rusted to the point of being weak such that the enclosure integrity can be compromised, repair or replace the part rather than painting it.

REPLACEMENT PARTS

Replacement parts are available from Maddox. While ordering parts, give a complete description of the part. Also, give the kVA, voltage, and serial number of the transformer, all of which may be found on the nameplate.

ADDITIONAL INFORMATION

Complete information on details of construction, installation, operation and maintenance can be obtained from Maddox.