Distribution Transformers Overview

Introduction

The distribution transformer business, partly originated in the Swedish ASEA stable in 1944 and within Desta Transformers, in 1953. Desta Power Matla, commenced operation in July 1999 in the original Desta Transformers premises in Booysens, Johannesburg. The other operation is situated in Cape Town (previously Power Engineers). In 2009, Desta Power Matla (DPM) joined forces with Powertech Transformers (PTT). At the same time, PTT’s shareholding changed significantly. Power Matla, DPM’s BEE partner of many years, increased its investment in the transformer industry by buying a stake in Powertech Transformers.
 

Technical Data

All our distribution transformers comply with SANS 780 and/or IEC 76, BS 171 and NRS 027.
 

Windings

All distribution transformer high voltage windings are made of copper. The low voltage windings are made of copper strip, but in certain ranges copper or aluminium foil is used. Diamond dot paper is used for interlayer insulation on the foil windings as this adds mechanical strength. Core and winding assemblies are clamped by means of top and bottom yoke clamps.
 

Core Construction

All distribution transformers cores are made of grain oriented, low loss magnetic cold-rolled silicon steel. Both sides of steel sheets are laminated with ceramic insulation. The core construction is optimised for cold-rolled steel properties so that best parameters for magnetic circuit are obtained, i.e. minimum no-load losses and small magnetising power.
 

Corrosion Protection

The exterior and interior surfaces of the transformer tank, cover and conservator (when fitted) are carefully degreased. Rust and millscale are removed by a process of acid pickling or phosphating.
 

The exterior surfaces of inland units are thereafter given a coat of high build primer, followed by a coat of high build alkyd base full gloss enamel giving a total dry film thickness of at least 75µm. The method employed is either flow coating or spray painting.

Coastal units are shot blasted and hot zinc metal sprayed prior to painting to a finish of 125µm.

The standard colour is Avocado colour C12 as specified in SANS 1097.
 

Processing

The complete active part is processed in an oven to obtain less than 0,5% moisture content. Within the prescribed time following the drying cycle, pressure is applied to the windings and the unit is tanked and filled, under vacuum, with heated, degassed and purified oil.
 

Cooling

On offer is a range of cooling methods such as ONAN, ONAF, or a combination thereof. Forced cooling can be activated by temperature or loading pattern.
 

Tanks

Hermetically sealed transformers incorporate a tank with corrugated or tube radiator fins.
The transformer tank has a sturdy design that allows for normal transportation of an oil-filled transformer without any damage resulting from vibration.
Free breathing transformers have fixed or removable panel radiators and isolating valves.
 

Quality Assurance

The transformers and miniature substations carry the SABS mark of approval. The distribution transformer factory Cape Town has the ISO 9001 version 2008 listing and as such a stringent quality assurance programme in accordance with the very specific requirements is rigidly adhered to. This ensures a product of the highest quality.
 

Testing

Routine tests according to SANS 780 are made on every transformer prior to despatch:

  • Measurement of winding resistance
  • Measurement of voltage ratio and verification of polarity and connection symbol
  • Measurement of impedance voltage and load loss
  • Measurement of no - load loss and no - load current
  • Induced overvoltage withstand test
  • Separate - source voltage withstand test
  • Measurement of paint thickness
  • Test for effectiveness of sealing

Type tests to SANS 780 can be undertaken on request:

  • Full impulse voltage withstand test
  • Full and chopped impulse voltage withstand test
  • Temperature rise test
  • Tank stiffness test

Special tests to SANS 780 can also be made on request

  • Short circuit withstand test (subject to limitations of SABS high current laboratory equipment)
  • Measurement of audio sound level

Quality Control

Vision

To be the number 1 supplier of transformers into our targeted markets.

Objectives

  • To improve the Test Success Rate.
  • To improve Unit On-time deliveries to 95% (3 month rolling average).
  • To reduce the Cost of Poor Quality (COPQ).
  • To reduce Work In Progress (WIP).

How we will achieve this:

  • By continuing to train all levels of supervision to be competent in leadership, interpersonal and technical skills.
  • By effective root cause analysis, prompt preventive action and cause elimination.
  • By enhancing on a continual improvement culture through quality awareness sessions, suggestion schemes, etc.
  • To embark on multi-skilling ; competence means doing the work right first time within the standards set.
  • By establishing departmental quality objectives supporting the company's global quality objectives and monitoring as per set framework at various functions and levels.
  • By ensuring that all forms of communication are effectively used throughout the entire organisation, supporting processes and quality.

Transport

Transformers are delivered to the customer fully assembled and ready for operation. During transport, transformers must be securely placed in vertical position and firmly fastened to prevent any displacement. The transformer undercarriage has small pulling eyes designed for ropes or fastening belts.
 

Warranty

All our products are backed by a 1 year warranty period.