The operational control of machines and automatic systems are performed by auxiliary (or control) circuits. Because of this function, these circuits must satisfy increasingly complex requirements. As a result, they must be particularly reliable, both in terms of function and safety against direct and indirect contacts. Auxiliary circuits can be powered directly from the network or through an isolation transformer. Unlike direct connection to power supply, the use of an isolation transformer allows the secondary circuit to have control voltage with no variations, even in the presence of unbalanced loads, thus ensuring greater safety of operation.
When an auxiliary circuit is powered by an isolation transformer, galvanic separation between the auxiliary circuit and the power circuit is successfully realized. In this way, an insulation failure of the auxiliary circuits does not affect the power circuit and, at the same time, the protection level against accidents and operational reliability is enhanced.
Working principle of isolation transformer
The isolation transformer does not change either the power or the voltage and current levels. Instead, it provides an extra degree of protection to the distribution system for those circuits that are set aside for access by other than engineering personnel and the circuits that are available for unspecified electrical apparatus.
In an isolation transformer, the primary voltage value will be equal to the secondary voltage and the two windings will have the same number of turns to compensate for losses.
Should one of these circuits have a catastrophic electrical casualty that prevents local circuit breakers and overloads from operating properly, the isolation transformer prevents a mechanical connection of the circuit with the rest of the distribution system. A catastrophic electrical problem will damage the transformer and allow time for the rest of the distribution system to react to the electrical problem. The isolation transformers effectively isolate these problem circuits from the rest of the single-phase distribution system.
The problems include:
- Capacitance build-up by high-frequency noise
- The unconditional ground connection between the primary and secondary
- Faulty components or power surges
- Earth leakage
The primary and secondary windings of an isolating transformer are electrically separated by a double or reinforced insulation, in order to minimize (in the secondary-side powered circuit) any risk.
Double isolation can be done by putting a metallic safety shield between the primary and the secondary windings and then connecting it to the ground. So, the electricity will flow to the ground in case of isolation damage and thus provide safety. Another method of double isolation is by using reinforced insulation and this type of insulation is made up of multiple layers, so if one layer breaks the next layer will provide the required safety.
Typical applications of an isolation transformer are telecommunication systems, data center supply systems, bypass lines protection, public buildings, and hospitals. It also helps to reduce the size and cost of power electronic components.
How does an isolation transformer protect people?
When someone touches the network without an isolated transformer, it will get an electric shock if it is at ground potential. Because the circuit completes itself over that person. However, if there is an isolated transformer in the network, even if the person touches the network, the reference voltage will not be ground, so the person who touches it will not be electrocuted.