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Power System Model

We offer you protection relay tests performed using a power system model

 

The power system model used in the DOHNÁLEK Company comes from the ZPA Trutnov laboratory from the time the latter was engaged in developing protection relays. It is a three-phase model taking the form of blocks. The protected object model is a testing device whose mathematical model is consistent with the protected object in terms of a protection algorithm.

 

 

When testing a protective relay on the model, it is not sufficient to have only a protected object model on its own. Protective relay performance is conditioned by its position in the electricity supply system. That is why the model takes on the form of blocks. Constructed as mobile units the individual blocks simulate the protected object or its part. We get a model of a requested part of the electricity supply system when we place and interconnect these parts properly.

 

The model´s rated values are 380 V and 20 A. It is equipped with voltage (secondary output 100 V) and current transformers (secondary output 5 A or 1 A). These ensure that the tested relay gets incoming signal which is the same as in reality. The protection relay itself doesn´t affect the model in any significant way as its rated capacity reaches 13.2 kVA.

 

The model verifies the protective function even in the protected object transient state, i.e. not only in the state of stabilized operation. Testing the relay using a model makes it possible to carry out tests and verifications equivalent to tests performed on the object directly.

 

Advantages of model testing as oppose to network tests:

 

		It is not necessary to single out a protected object with a tested relay from an
		electricity supply system and thus restrict its operation.
		Testing the relay on the model does not affect the network operation. In addition,
		we cannot ignore the fact that the tests "for real" carried out in the network can
		cause a real accident. Although the probability is low, the consequences would be
		very severe.
		The model enables unlimited repetition of functions and tests of a relay in the
		selected conditions which is not possible in case of "for real" relay tests in the
		network. Such repetition in the network not only causes extraordinary overcharge but
		also reduces the operating life of a tested machine or a device. This model is thus
		suitable for repeated tests with frequent changes of parameters.
		Compared to secondary relay tests, this alternative has an advantage of a better and
		clearer provability. Secondary tests are carried out only in the stabilized state and in
		one theoretically derived ideal set of conditions and parameters. Model´s current and
		voltage correspond to reality far better even in terms of all three phases.

 

 

A model contains following blocks:

 

Circuit breaker		Circuit breaker model, modelled by a contactor and relay automatics,
		allows for electric control through a protection relay or auto-reclosing
		(single-pole and triple-pole) as well as a push-button hand control.
Short-circuit device		It allows a choice of all kinds of short-circuits, i.e. RS, ST, TR, RN, SN, TN
		and RST.
Block turbine - generator		Generator is modelled by a synchronous machine with the possibility of
		excitation control. Turbine with direct current drive with power or speed
		control.
Line		Line impedance can be chosen in parts of 1% of nominal impedance Zn.
		The earth ratio coefficient Zg/Z1 and line impedance angle Φ can also be
		chosen.
Load		Reactive component of the load is modelled by a three-phase control
		transformer, active component by three resistors.
Current and voltage transformers		Sets of voltage and (380/100V) and current (20/5A or 20/1A) transformers.