DE19621567C2 - Controllable loading device - Google Patents

Description

The invention relates to a controllable loading device for generating electricity in a three-phase network.

With an earth current directional relay in a three-phase system (especially near generators in busbars circuit) there is often the problem that the existing earth currents are not sufficient to excite or trigger the relay chen.

It was therefore in practice in the past of the fene delta winding of a transformer a motor controllable resistor with tap for generating an earth current in the three-phase network. When a Displacement voltage, the resistance value was then so far continuously decreased until the desired earth current to Triggering of the relay was given. This arrangement is very elaborate and expensive, the resistance is not for everyone application cases can be used.

The invention has for its object a device for increasing the earth current for an earth fault direction relay specify, in which the disadvantages mentioned above are eliminated and the increased earth current is at least the smallest Should reach the setting value of the earth fault direction relay, see above that even low earth currents can be detected safely and selectively.

According to the invention, the solution is a controllable loading Load device according to the features of claim 1.  

This setup is simple with standard components feasible, with a good time ver hold is given. The decor is flexible from small up to large currents, in particular from 0.1 A to 400 A, especially 1 A to 300 A can be used in the secondary winding. Be A standard is preferred for the automation device dard product in modular technology, e.g. B. a memory programmer bare device used.

The resistors are advantageously dual or binary switchable. This makes the change in resistance very easy designed. For this, simple output relays of the car Automation device can be used.

It is beneficial if the resistances depend on the displacement voltage occurring at the secondary winding controls are. This is a good adaptation of the earth current to the input sensitivity of the earth current directional relay possible, the security against the state of the release Technology is improved. For measuring the zero sequence voltage can analog input modules or modules of the automation tion device are used.

The earth current is preferably used to excite an earth current converter relay, which ensures safe tripping and safe  Error detection is given. The selectivity of the earth fault registration is fully guaranteed. A preferred type Use of the device is the earth fault direction detection for generators in busbar connection (as in the Drawing shown).

Embodiments of the invention, further details and before Parts are shown below using the drawing as an example explained in more detail. Show it:

Fig. 1 means a three-phase mains with connected load,

Fig. 2 and 3 connecting images of the loading device with switchable resistors,

Fig. 4 is a characteristic diagram for switching behavior of the loading device,

Fig. Stungseinrichtung Tables 5 and 6 for logical switching behavior of the loading and

Fig. 7 is a block diagram for the interconnection of the logical modules (software or network blocks) of the loading device.

In Fig. 1 a three-phase network arrangement is shown in which two generators G1, G2 are electrically connected to a network N. In the corresponding connection lines, switching elements for separating and connecting the electrical connections, in particular circuit breakers LS, are interposed.

The respective generators G1, G2 are earth currents Directional relay R1 or R2 assigned. These get over  each assigned current transformer SW current signals of the resp generators G1 and G2 for earth current detection.

With particularly low earth currents it is often a safe one Tripping by the earth current directional relays R1, R2 not always possible. Therefore, in the present case there is a loading device B provided that serves to increase the earth current.

The loading device B first includes one connected to the network N connected transformer Tr, which is at least one second the winding S1. The secondary winding S1 is of fene triangular winding to which a controllable Wi the combination W can be created. This will follow also referred to as resistor W.

The resistor combination W comprises a predetermined number of partial resistors not shown in this FIG of switching elements can be combined. The switching links are controlled by an automation device A. The partial resistors have resistance values of playful under one ohm, especially between 0.75 and 0.05 ohms.

The partial resistors are preferably switched in two stages, the respectively generated resistance combination W depending of the ver occurring at the secondary winding S1 storage voltage is controlled. The automation can do this tion device A, if necessary, measured value inputs for detection the zero sequence voltage at the secondary winding S1 point.  

A automation device A is preferably used Programmable automation device with modular used input and output modules. Such Establishment is generally known to the specialist under the name "Simatic" known. Such an automation device (Simatic control A) can be easily programmed or parameterized the so that the realizing function of the earth current increase is easily possible.

See also FIGS. 2 to 7.

The operation of the entire device is explained in more detail below with reference to a technical functional description with reference to FIGS . 2 to 7. The figures and the functional description complement each other. Variable Load Resistor Unit (VLRU)

The default is:

Detection of earth faults, the displacement voltages in the Cause three-phase network and between 20-100% of Lei ter / earth voltage. For selective earth fault detection a zero current is required, which is at least the smallest Setting value of the earth fault direction relay of 0.002 xIn exceeds (corresponds to 190 A on the E-transformer secondary side).

When a displacement voltage occurs in an isolated This zero current must be generated in the grid. That happens with an ohmic resistance depending on the occur the displacement voltage. But since with a Erdstromerzeu supply device only limited currents for the primary side  to be produced is an adjustable load resistance required.

In the present circuit, a binary staggered loading resistor W, consisting of four elements or partial resistors T, is used, which are short-circuited as required by powerful switching elements, in particular contactors SG. The control of the SG contactors takes place depending on the level of the displacement voltage with an automation device known under the name "Simatic S5" A. The use of three SG contactors results in a gradation of the load resistance W in 2 ³ = 8 steps, which - depending of the occurring displacement voltage (U _o ) - can be short-circuited. The generated earth current is kept almost constant.

The inputs of the Simatic control A are as follows wired:

The digital inputs DE are controlled via auxiliary relays 125 V ~ with an excitation signal from the 7RE26 (F421 + F422) of the transformer protective cabinet and from the generator switch position of the generator branches GS. These DE inputs are indicated by LEDs on the module. Analog inputs AE are controlled by the transducers for U ₀ and I ₀ . The U ₀ transducer is connected to a 5: 1 voltage divider (3PP13). The I ₀ transducer is connected to a small current transformer (4NC12).

The blocking or reset input on the digital input construction group can be activated by pressing a light button and right turn can be controlled. A white signal lamp signals blocking the VLRU.

The outputs of the Simatic control A control the three auxiliary contactors H, the contacts of which actuate the powerful contactors SG (460 V, 60 Hz). Because of the high current load, three contacts (90 A each) are connected in parallel and short the load resistance elements or partial resistors T in a predetermined manner (see also FIGS. 4 to 7).

In addition, the following signals are wired to the terminal strip.

• - Failure not in protection zone Protection zone)
• - Pick-up + U ₀ too low (= protective relay activates but load does not measure U ₀ )
• - I ₀ too low.

All of the above output signals are on the relay module signaled via LED.

Description of the signal flow

The entire control or load device B is started via the protective excitation of the respective 7RE26 (earth fault or earth current direction relay not shown in more detail) and the switch-on message of the relevant generator switch (LS) (network N1). If the CB is not switched on, no earth current needs to be generated when the pickup is activated. Earth fault is then detected via U ₀ measurement, a trigger signal then being sent with a time delay.

If these conditions are met, a time stage t _{1 is} started (network 2).

In addition to the earth fault relays, the displacement device B measures the zero sequence voltage at the transformer Tr via a transducer (network N1). The time stage t ₁ (network N2) covers the settling time of the U ₀ transducer of approx. 0.4 s. After t ₁ has elapsed, a query is made as to whether U ₀ exceeds the minimum value (network N2).

T ₁ is a cycle time, after the end of which it is checked whether the condition U <Umin (<100 V) is fulfilled.

The excitation signal is sent to an AND gate via network N4 leads, which also evaluates the negated U <Umin signal and possibly to the message: "Excitation and U <" leads.

If the condition: "excitation and U <" is met, a flip-flop starts and thus the time stage t ₂ (network N3). This is used to monitor whether there is an external fault after the time has elapsed or not (t ₂ ≈ 4 s). At the same time, the condition for activating the contactors SG is maintained during this time. The SG contactors are only excited during t ₂ !

A pulse is generated in parallel with t ₂ and the time stage t ₃ (network N6) is started. The pulse transmits the enable for the voltage evaluation of the CPU. The applied voltage is only evaluated and saved during the one-time pulse. Changes in the U ₀ voltage are no longer taken into account. The pulse resets the signal "I ₀ too low" via an OR so that the current is evaluated and reported during the measuring process. As soon as the starting conditions of the 7RE26 or the generator switch position no longer apply, the memory modules N3 and N4 are reset.

The time stage t ₃ (network N6) covers the settling time of the current transducer of approx. 0.4 s. The time step and the current query are linked via AND. They thus form the message: "I ₀ too low" (I <190 A).

Reference list

Network
Circuit breaker
G1, G2 generator
R1, R2 earth current directional relay
Trtransformer
Bloading device
AAutomation facility
S1, S2 secondary winding
SW current transformer
Resistance
I ₀

Earth current
U ₀

; Displacement voltage
SG contactors or switching elements
Partial resistors
DEDigital inputs
AI analog inputs

Claims (2)

1. Controllable load device (B) for generating earth current, ie for increasing the earth leakage current (I ₀ ), in a three-phase network (N), with a transformer (Tr) which can be connected to the three-phase network (N) and which has a secondary winding (S1). has in an open delta circuit to which a controllable resistor (W) is connected, the resistor (W) being a combination of partial resistors (T) which can be combined with one another by switching elements (SG), and wherein the switching elements (SG) are controlled by an automation device (A), and the partial resistors (T) are controlled as a function of a displacement voltage (U ₀ ) occurring on the secondary winding (S1), such that the associated earth fault directional relay (R1, R2) triggers / triggers reliably. 2. Controllable loading device according to claim 1, wherein the partial resistors (T) are switched in two stages.