Langley Engineering Ltd - supplier of electrical equipment to the medium voltage distribution industry for more than 25 yrs.
 
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Pad Mount Transformers

The term ‘Pad Mount Transformer’ has become a generic expression for a low kVA ground mounted transformer with its own protection and even switching options either via elbow connectors or built in sectionalising switches. Such devices have been the norm in America for 25 years since the URD revolution. Now they are finding favour in Europe primarily to replace pole mounted transformers in rural areas but also in urban areas where traditional substations with ring main switchgear and LV distribution panels are considered an overkill. These transformers have their own protective fusing and this comprises a low energy Bay-O-Net fuse located in the high voltage compartment with a back-up high energy current limiting fuse in series. Both fuses are oil immersed.The Bay-O-Net fuse protects against secondary faults and transformer overload and is a field replaceable device.
  
The back-up CL fuse will only operate in the event of a transformer failure hence it does not need to be field replaceable. Some utilities are also requiring conventional LV fusing in these transformers which is readily achieved – up to two outgoing ways – also with generator connection facilities. The use of polymeric cable and loadbreak elbows enable switching and isolation to be carried out in the HV chamber in what is known as a ‘Dead Front’ environment , ie all termination's are fully screened and watertight. The Pad Mount Transformer would normally sit on a concrete ‘pad’ however the small 1Ø designs are now available already mounted on a ‘polypad’ base so they come ready to be sited on some hard standing, connected and switched on.
 
The Cooper Power Systems single phase 50KVA pad mount transformer shown was installed to replace a pole mounted transformer that had been fed by an overhead line. The very beautiful rural aspect of the hamlet was improved significantly by removing the line. In tank bay-o-net fuses offer protection and the loadbreak elbows can be readily disconnected for isolation, earthing or testing. They also make life very easy too, should you need change or quickly upgrade the transformer.
 
This Utility has worked with Cooper Power Systems to develop their own customised design of single phase pad mount transformer. This design comes on its own fibreglass pad ready for installing on to hardcore or paving, secondary fusing coordinated with the primary fusing is also included.
 

The Utility installing these 3Ø transformers discovered that due to the large thermal capacity of the design they can use a 200KVA unit where previously they needed to use 315KVA. Note the special security of the cabinet, there are no external nuts or bolts to be accessed. The Low voltage compartment is protected by padlock and a further special key and the HV has yet a further padlock accessed via the LV only.
 
Langley Engineering Ltd - Medium Voltage Equipment for the Electricity Industry
16 The Markham Centre, Theale, Reading, Berkshire RG7 4PE - Tel: 0118 9305990