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Our Other Power Transformer Products

Variable Transformers

When testing or repairing electrical or electronic equipment, a variable auto transformer or “variac” is a valuable addition to your test bench. Variacs are useful in preventing damage to equipment which may result from direct connection to the mains supply. They enable you to slowly raise and lower the input mains voltage when testing electrical equipment. Variacs also provide a simple and robust method of adjusting voltages such as when using hot-wire or plating equipment.

A variac can be used to control the primary of an isolating transformer, thus providing isolation from the mains. This can be particularly useful for controlling low and extra-low voltages.

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Variable auto transformers are essential equipment for electricians and electrical contractors. Applications include:

  • Control of AC voltage and current for testing
  • Voltage and current control for rectifiers (as used in electro-plating and precious metal recovery)
  • Motor speed control
  • Lighting and heating control
  • Appliance testing – enables gradual voltage increase
  • Over and under voltage testing
  • Panel or bench mountable voltage control
  • Motorised control of voltage and current

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Southern Electronic Services (SES) is able to supply:

  • Single phase bench or panel-style up to 28A
  • Three phase bench-style up to 28A
  • Motorised single and three phase Variacs up to 28A
  • Metered (digital or analogue) Variacs – 10A rated

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Advantages of our Variable Auto Transformers

  • Most sizes available within days
  • Robust construction
  • Clean sinusoidal waveform
  • Smooth control throughout range
  • Low load regulation
  • Linear output – unlike solid state dimmers
  • Extremely low field – unlike TRIAC control which can result in waveform distortion and harmonics

SES can supply a wide range of single-phase and three-phase variacs.

Potential (Voltage) Transformers

Potential transformers (also known as voltage transformers) are used in electrical measuring instruments and electrical protection devices.

SES can supply both a single and three-phase potential power transformer with short notice.

Advantages of our Potential Transformers

SES has designed and built many potential transformers over the past 30 years. Our products boast these features:

  • Fast turnaround of a custom potential transformer – often within days
  • Australian Standard AS1243 – 1982 compliant
  • Available in a wide power range – from 10VA to 500 KVA
  • Optional electro-static screen between primary and secondary windings
  • Robust construction
  • Choice of voltages
  • Choice of mounting brackets
  • Terminal blocks or flying leads
  • Tough varnish coating in clear or black
  • Insulation classes up to class H – 180°C

A typical three-phase potential transformer may be specified as follows:

Specification: Three Phase Potential T/F 415v 50-60Hz / 110v @ 3VA/Ph Burden (4-wire STAR) (4-wire STAR).

Standard: Designed to comply with AS 1243-1982: “voltage transformers for measurement and protection”.

Construction: Open type chassis mountable, double-wound voltage transformer, constructed using high-efficiency grain-oriented E-I laminated core for protection application. Primary and secondary terminated to terminal blocks, and input and output star points earthed.

Burden: 3VA / phase
Ratio Error: < 0.5%
Temperature Class: Materials rated at 120°C minimum
Class of Accuracy: 1.0 P (1%)
Rated over-voltage factor: Fv = 1.9 (designed to operate at 1.9 times primary voltage)
Overall Dimensions: H x W x D = 150 x 150 x 60mm
Weight: 5k


An inductor, which is commonly referred to as a choke, is a current limiting and smoothing device. Chokes store energy in the form of a magnetic field, which may be AC or DC.
Chokes are used in power supplies, audio amplifiers, welders, variable speed drives, uninterrupted power supply (UPS), audio speaker cross-overs and inverters.

Reactors are a type of inductor used to limit the starting current to large electrical machines. These reactors can be either single phase or three phase.

SES manufactures wound inductors and reactors ranging in size from less than 1kg to hundreds of kg. We can supply:

  • Single-phase chokes and reactors
  • Three-phase reactors
  • Air-cored chokes
  • C-core and E-I construction

Advantages of our Inductors

  • Australian Standard AS61558 – 1997 compliant
  • Fast turnaround of custom chokes and reactors
  • Robust construction
  • Choice of inductance and current ratings
  • Choice of construction type – shell or core
  • Choice of mounting brackets
  • Terminal blocks, flying leads, or lugs (depending on current)
  • Tough varnish coating in clear or black
  • Available in a wide power range
  • Insulation classes up to class H – 180°C
  • Quiet operation

DC Power Supplies

Despite Australia’s mains electricity supply being 240vAC 50Hz (alternating current), most of our electronic equipment uses DC (direct current) power. For example, a stereo amplifier usually operates at about 30vDC. To obtain that 30vDC from our 240vAC mains, that amplifier needs to have a DC power supply inside it.

There are a number of types of DC power supply that can be provided and Southern Electronic Services is able to supply the following:

Switch Mode

Small and light for their rated power output, switch mode is a very popular choice of DC power supply. The Meanwell range is extensive, including single and three phase, DIN rail or chassis mountable, multiple outputs, UPS and battery chargers.


This is the most basic type of DC power supply. It consists of a transformer and rectifier. We can supply single and three-phase un-filtered DC power supplies. Three-phase power supplies are very useful for heavier currents, above 10A and up to thousands of amps. Six-phase diametric star output results in an efficient DC power supply.


This DC power supply consists of a transformer and rectifier with a filter added. Available in single and three-phase configurations, filtering can range from just a capacitor across the output, to a filter network with chokes and capacitors.

Filtered power supplies have high surge capacity and can make an extremely robust and reliable DC power supply. As with un-filtered DC power supplies, the output voltage will vary with the load current.

Linear Regulated

This consists of a filtered power supply with the addition of a voltage regulator to ensure the output voltage remains constant under load. Available in single and three-phase configurations, regulated DC power supplies are usually larger, heavier and more expensive than switch-mode supplies, but are more robust and reliable, and have high surge capacity.

We have made linear regulated power supplies for the control systems on ferries (these were single-phase 240v 50Hz / 24v DC & 100A linear regulated power supplies).

Zig-Zag Transformers

A zig-zag transformer is a special-purpose power transformer with a zig zag or “interconnected star” winding connection. Each output is the vector sum of two phases offset by 120°. Zig-zag transformers are used to create a missing neutral connection from an ungrounded three-phase system to permit the grounding of that neutral to an earth reference point.

These transformers are also used for harmonic mitigation as they can suppress triplet (3rd, 9th, 15th, 21st) harmonic currents to supply three-phase power as auto transformers (serving as the primary and secondary with no isolated circuits), and to supply non-standard, phase-shifted, three-phase power.

For more information on our power transformer product range, phone (03) 9706 4202 or contact us online.