Choosing the right isolation transformers for power distribution projects

Most modern UPS systems do not include the internal transformers that were present in earlier designs. This evolution has increased the demand for isolation transformers while reducing the weight and size of UPS systems

By Baishakhi Dutta

In the new transformerless UPS system designs, the transformers are optional and, if used, can be placed in the best location to achieve a required result. The best example of this are the isolation transformers, which are used to transfer electrical power from a source of alternating current (AC) to some equipment or device while isolating the powered device from the power source, usually for safety reasons.

Why isolation?
Isolation transformers provide a specialised function. These are the most primary type of transformers used in industries, supplying power to sensitive devices/equipment.
In electronics testing, troubleshooting and servicing, an isolation transformer is a 1:1 power transformer, which is used as a safety precaution. Since the neutral wire of an outlet is directly connected to the ground, grounded objects near the device under test (like the desk, lamp, concrete floor, oscilloscope ground lead, etc) may be at a hazardous potential difference with respect to that device. By using an isolation transformer, the bonding is eliminated, and the shock hazard is entirely contained within the device.

Various types

• AC isolation transformers
• Drive isolation transformers
• Medical grade isolation transformers
• Three-phase isolation transformers
• Custom isolation transformers

Application areas
Most common isolation transformers are used where there are very sensitive instruments that need protection from the ‘noise’ on the grid. The classic examples are heart monitors in hospitals and other medical equipment. The monitor is usually plugged directly into the isolation transformer before even connecting to the UPS. Since probably 95 per cent of UPS units are of the ‘buck and boost’ type, with the battery floating in parallel to the rectifier inverter connection rather than in series between the rectifier and inverter, the UPS system’s grounding makes the unit useless for the isolation of harmonics.

Safety always
Isolation transformers make working on AC equipment safer and offer protection against shorts in the circuit. Working on the principle of mutual induction, they are used to break ground loops and remove unintended current paths where accidental contact could cause problems. When choosing an isolation transformer, select one with the appropriate ratings and specifications for your requirements.

A few companies that offer isolation transformers

Servostar India Pvt Ltd
Servostar isolation transformers are designed to meet ISO 2026 guidelines.

Key features

• Phases – Single phase
• Input voltage – 220V
• Output voltage – 220V
• Frequency – 50Hz
• Power factor – 0.75 lag to lead
• VI electric strength – 1500V AC for 120 seconds
• Insulation resistance – More than 100M ohms
• Ambient temperature – 1˚C- 50˚C

Contact: www.servostarindia.com

Volina
Volina is an ISO 9001-2008 certified isolation transformer manufacturing company.

Key features

• Output voltage – 220V in single phase; 415V in three phases or as per requirement
• Input voltage – 220V in single phase; 415V in three phases or as per requirement
• Ratio -1:1
• Cooling – Air/oil
• Capacity – 0.5kVA to 1000kVA

Contact: www.volina.in

VENER7
The VENER7 power line noise isolator range employs a unique multiple shielding technique that reduces the inter winding capacitance to below 0.009 pf and DC isolation to over 100M ohms. Attenuation of common mode noise is about 100dB. Regulation at 400V or 415V AC is about 4 per cent.

Key features

• Filters power line noise, spikes and transients
• Isolates sensitive equipment from noisy power lines
• Complete electrostatic shielding
• Minimises common mode noise by over 130dB
• Minimises transverse mode noise
• Line and load regulation better than +3.5 per cent
• Quality components, energy-conserving ratings and a rugged design ensure good long term value

Contact: www.vener7.com

Narendra Enterprises
The organisation is engaged in offering a wide range of quality isolation transformers that come in a compact size and offer uninterrupted performance.

Key features

• Power factor: 0.9 to 0.98
• Efficiency: 80 – 99 per cent
• Voltage regulation: 16 – 1.6 per cent
• Temperature rise: ≤85°C

Contact: www.narendraenterprises.in