Isolating transformer
In the narrower sense, an isolating transformer is a mains transformer which transfers the mains voltage in a ratio of 1: 1 to a secondary winding, which is separated from the mains voltage and ground potential by means of a so-called protective separation ( galvanic separation ). This is achieved through reinforced or double insulation .
Designs
There are single-phase isolating transformers, usually designed for 230 V in Europe, and isolating transformers for three-phase alternating current for the 400 V common in Europe.
In general, each transformer with separate windings is an isolating transformer with galvanic isolation between the windings, which are usually superimposed to save space, between which there is insulation of sufficient electrical strength, but mostly low mechanical strength. This is not considered to be sufficiently safe for personal protection. In the case of isolating transformers according to the standard, the primary and secondary windings are housed in separate winding chambers on the magnetic core .
Applications
The terms isolating transformer (power engineering) and isolating transformer (communications engineering) should not be confused, as transformers and transformers are developed from different perspectives. Isolation transformers are built for optimal energy transmission at one frequency (mostly 50 Hz or 60 Hz), whereas transformers are mostly designed for broadband signal transmission and high linearity. In the case of transformers, bifilar or trifilar windings are usually used, which ensure an expansion and linearization of the transmission range. Isolating transformers are used for low-frequency signals in order to avoid galvanic isolation to avoid earth loops and the associated hum interference and - if necessary - to establish a mains isolation. Here and in communications engineering, these "transformers" are called transmitters .
Network isolating transformers are used to isolate energy networks from one another. They are often used in workshops and laboratories, for example, to be able to carry out repairs and experiments safely, as well as to operate all-current devices in order to reduce the risk of electric shock when working on devices or equipment supplied with mains voltage :
An output voltage that is not connected to earth is generated , the potential difference to earth can assume any value up to insulation strength (usually 4 kV) without a current flowing through the body to earth when a single conductor is touched on the secondary side.
Isolating transformers are designed as toroidal transformers, and any output AC voltage of typically 0-300 V can be picked up with an adjustable slider. In addition to the function as an isolating transformer, an undervoltage and overvoltage situation can be specified for an assembly to be examined. Compared to a network simulator , the curve shape and frequency cannot be influenced.
Isolating transformers are also used in medical technology and for ungrounded operation of measuring devices whose inputs or outputs are related to the housing / protective conductor potential.
safety instructions
- Isolation transformers do not protect against electric shock if both output poles of the secondary side are touched at the same time.
- Isolation transformers do not protect against high voltages above their insulation strength (for example the picture tube anode voltage).
- An in-house installation of RCD acts not on the devices connected to the isolation transformer on the secondary side consumers .
To ensure protection, there must be no electrical connection between the secondary side and earth potential or the protective conductor or other conductors on the primary side. As a result, no current can flow in the event of a single-pole, faulty earth contact, for example via a person who is at earth potential and touches a conductor on the secondary side. The transformer core can be grounded.
When connecting two devices to the isolating transformer, the housings of the consumers must be connected to an ungrounded equal potential ( ungrounded local equipotential bonding ). In repair shops, however, each device must be connected to a separate isolating transformer.
See also
literature
- Günter Springer: Expertise in electrical engineering. 18th edition, Europa-Lehrmittel , Wuppertal, 1989, ISBN 3-8085-3018-9 .
- Paul E. Klein: Mains transformers and chokes. 5th revised edition, Franzis, Munich, 1979, ISBN 3-7723-1065-6 .
- Peter Bastian, Horst Bumiller, Monika Burgmeier, Walter Eichler, Franz Huber, Jürgen Manderla, Jürgen Schwarz, Otto Spielvogel, Klaus Tkotz, Ulrich Winter, Klaus Ziegler: Electrical engineering . 26th, revised and expanded edition. Europa-Lehrmittel, Haan-Gruiten 2008, ISBN 978-3-8085-3160-0 .
Web links
Individual evidence
- ↑ IEC / EN 61558-2-4: 2009; Special requirements and tests for isolating transformers and power supply units that contain isolating transformers.