JPS63310348A - Short-circuit detection device for excitation circuit - Google Patents

Abstract

PURPOSE:To judge whether an excitation circuit shorts or not, by detecting current pulsation on the primary side of an induction machine. CONSTITUTION:An induction machine 1 is excited by a cycloconverter 2 and performs delivery and acceptance of power with a system 5. A current transformer 10 for meter is provided on the stator side of this induction machine 1, the signal of which is inputted into an excitation circuit short-circuit device 7. This output signal is led to a current amplitude measuring device 8 through a filter 6. At the time dividing a cycle in twelve equal parts, the current amplitude measuring device 8 samples an instantaneous value of the current, equalizes its absolute value and finds out the current amplitude I. The current amplitude I is sampled by a pulsation discriminator 9, with which the pulsation is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a short-circuit detector for an excitation circuit of a three-phase AC-excited supersynchronous Servius induction machine, and more particularly.

The present invention relates to an excitation circuit short circuit detector suitable for detecting short circuits in the excitation circuit of an induction machine whose excitation circuit is current-controlled.

[Background of the invention]

In recent years, three-phase AC-excited super-synchronous Servian-controlled wound induction machines have attracted attention, but the excitation current for these machines is usually adjusted to match the required current. Referring to FIG. 2, in FIG. 0, which explains short-circuit detection in a conventional excitation circuit,
Excitation current is supplied by a cycloconverter 2 equipped with an excitation transformer 4. This exciting current is a three-phase alternating current with a slip frequency, and if a short circuit occurs in this exciting circuit, in addition to the current from the cycloconverter 2, the rotor 1
The voltage induced in 2 also causes an excessive current to flow, causing damage to the lead wires and rotor windings.

To prevent this, for example, Japanese Patent Laid-Open No. 57-14216
There is a short circuit detection device as described in Publication No. 4. This detection device takes in the signal of the CT 13 and detects its imbalance, and is similar to the detection device 14 shown in FIG. 2. Furthermore, in the sense that the three-phase balance is broken, a CT is provided to detect the neutral point current, and a detector 15 is also used to detect the overcurrent.

However, when the cycloconverter 2 performs current control, the cycloconverter output current does not change even if a short circuit occurs. Therefore, it is possible to detect a short circuit between the cycloconverter 2 and CT13 as shown in A, but it is difficult to detect a short circuit that occurs in a place far from CT13, such as in the slip ring or rotor winding of an induction machine. Met. Furthermore, CT is a direct current CT to detect low frequency current.
The problem is that it is expensive and takes up a lot of space.

[Purpose of the invention]

An object of the present invention is to provide a short circuit detection device for an excitation circuit that can detect a short circuit even when the excitation circuit is under ffi flow control and does not use an expensive DC CT in the excitation circuit.

[Requirements for invention]

The present invention prevents line-to-line short circuits in the excitation circuit from occurring on the primary side of the induction machine.
! By focusing on the generation of flow pulsations and power pulsations and detecting them, short circuits in the excitation circuit are detected.

This phenomenon was also measured in model tests, but theoretically,
Explain briefly. In Fig. 3, the first rotor winding 16 has a slip S! When the stator side frequency is fO, an excitation current with a frequency of sfo is flowing. Normally, when viewed from the rotor side, the current is a positive phase current (rotating in the direction of rotation) in which U, V, and W are each shifted by 120 degrees. As a result, the frequency (1-8)io corresponding to the rotational speed of the rotor is made to match the frequency of fo on the stator side as fixed rotational speed excitation.

If a short circuit occurs in this state, the balance of the excitation circuit current will be lost, and the frequency sf as seen from the rotor side.

This produces negative sequence current and zero sequence current. This zero-sequence current is
Although the effect on the stator side is small, the negative phase current induces a current with a frequency of (1-28)fo on the stator side as fixed rotation speed excitation. If this value is Iz and the positive phase component is Il, then the stator current is: Ixcosfot+Izcos (1-28) fat Changing this equation, Il"+(z"+2 ItIzcoszs fot,
When cos(fot+a)S(1, α(1, and after all, the amplitude is 2sfoj=O when I *ax=
When I t + I Z2sfot=π Imt
n=II Iz, and as shown in Figure 4, the current with the frequency fo pulsates at the frequency 2sfo, and the maximum value I wa
It can be seen that x s minimum value I min. When a short circuit occurs, this negative sequence current becomes 50% or more of the positive sequence current, so if this pulsation is detected, a short circuit in the excitation circuit can be easily detected.

However, since this current may change suddenly when the load changes, it is important to use a detection device that focuses on the periodicity of pulsation.

The present invention detects a short circuit in an excitation circuit by measuring the current amplitude or power and detecting that the current amplitude or power pulsates more than a predetermined number of times.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 1 and 5. In FIG. 5, the induction machine 1 is excited by the cycloconverter 2 and supplies power to the system 5, or
Power is supplied from.

An AC CTl0 is provided on the stator side of the induction machine 1, and its signal is input to the excitation circuit shorting device 7.

The contents of this excitation circuit short circuit device 17 are shown in FIG. This current is guided through a filter 6 to a current amplitude measuring device 7. To measure this current amplitude, as shown in Figure 6, the current amplitude is obtained by sampling the period of the instantaneous current value i (t) over a period of m (m), and averaging the absolute values. The value is sampled by the pulsation determiner every Δts shown in FIG. The first Nisan horse pull is stored as IO, If without being judged as a local maximum value or a local minimum value, and from the next sampling, the sampled at that point is Ih + 1, and Ik-1゜Ih, I
From h+1, it is determined whether or not k is the maximum value.

This discrimination method is the minimum value when Ih is smaller than Ik-1rIh''t, Ih is Ih-t, Iha
When it is larger than t, it is determined to be a local maximum value. For example, if it is determined in step S2 that the value is a maximum value, that value is set as I m&X in step S4. This X is
In step S6, the difference from the previously determined ImLll is calculated and the difference is set as Δ■.5 Next, in step S7, Δt is set to a preset value (ΔI).

If it is smaller than that, return to step S1 and perform the next sampling.If it is determined in step S7 that ΔI is larger than (ΔI)o,
In step S8, the number of times n and the time tn are stored. In step S9, if the time difference between the first time and the (n-1)th time is greater than the predetermined time Δl, step S10 resets n and returns to step S1 again. In step S9, the n-th time and (n −
1) When the time difference from the second time is smaller than a predetermined time Δt1, the number n is compared with the number no preset in step Sll, and if the number n is greater than the set number nQ, the excitation circuit is Detect short circuit. Hereinafter, how this device operates with respect to the current patterns shown in FIGS. 8 to 10 will be explained. FIG. 8 shows that the current is approximately constant during normal steady operation, and in this state, in the present embodiment shown in FIG.
In step S3, neither the maximum value nor the minimum value is determined, and even if there is slight pulsation, it is not determined to be pulsation in step S7, so it is not determined to be an excitation short circuit. In the 0th order, as shown in FIG. 9, the current is monotonous. If it decreases or increases monotonically, it is not determined to be a local maximum value or a local minimum value in steps S2 and S3, and an excitation short circuit is not determined. Furthermore, even if these are repeated over a long period of time, such as during long-term power adjustment, the difference between the local maximum value and the local minimum value is large at that time, and YES is determined in step S7, but the next The extreme value is (Δ
tz), YES in step S9.
It is determined that this is the case, and is set by the SIO, and it is not determined that the excitation circuit is short-circuited. Next, the operation of this embodiment will be described with respect to a phenomenon when the excitation circuit is short-circuited, as shown in FIG. 10, similar to that shown in FIG. 4. A short circuit occurs in the excitation circuit at time A, and after that, at time 0 B, where pulsations are repeated at twice the slip frequency, in this embodiment, it is determined to be the maximum in step S2, and steps 34, S6. S
7. S8. At time C of the 0th order, where n=1 at S1o after passing through S9, it is determined to be the minimum value at step S3,
Step S5゜S6. S7. After passing through S8, n=2. If the setting value no=2, in this case, step S
ll is determined as No, and the process returns to step S1 again. Next, at the time of day, the process returns to step S1.
2 is determined to be the maximum, and the following steps S4 to S5. S6.
S7. After passing through S8 and 89, n=3. Step Sl
In case 1, since no=2, it is determined as YES, and a short circuit in the excitation circuit is detected.

It can be seen that this device does not malfunction even in the steady state shown in FIG. 8, or in the power adjustment or power fluctuation states shown in FIG. 9, and operates only when the excitation circuit is short-circuited as shown in FIG. 10.

The current amplitude measuring device 8 is not the one shown in FIG.
Exactly the same effect can be obtained with the analog circuit shown in FIG.

Another embodiment of the present invention will be described based on FIG. 11. In this case of blindness, the slip frequency sfo is read in step S13 from the frequency-voltage converted signals from all the detectors of the wound induction machine. This reading is performed before the execution of step S9, and 81 to 81 not shown in FIG.
Since S8 is exactly the same as the embodiment shown in FIG. 1, by selecting Δ1 in step 12 to be approximately 1/4 sfo, the time difference between the maximum value and the minimum value can be selectively set to twice the slip frequency. It is detected only when it corresponds to period 172 corresponding to the frequency of . In this way, only the 1/2 s fo component of the pulsation period shown in FIG. 4 can be extracted, and malfunctions can be reduced.

Another embodiment of the present invention will be explained with reference to FIGS. 12 and 13. In this embodiment, the current amplitude is used as a pulsation detection means, and the sine and cosine of the double slip frequency are and perform multiplication.

When they are integrated over time by the integrator 23, 2sf
Components other than the o component become smaller, and again, selectively 2s
The fo component can be detected. This method is easy to configure using analog circuits.

In the previous embodiments, only the excitation circuit short-circuit detection device using current amplitude was explained, but as shown in Fig. 9, detection can be performed in exactly the same way even if the power value is used instead of current amplitude. can. In the case of electric power, the electric power P may be calculated by also taking in the instantaneous value of the voltage ° as a data input.

〔Effect of the invention〕

According to the present invention, it is possible to detect a short circuit in the excitation circuit of an induction machine whose excitation is current-controlled, and the conventional excitation-side DC C'r can be omitted.

[Brief Description of the Drawings] Fig. 1 is a flowchart of an embodiment of the present invention, Fig. 2 is a conceptual diagram of a conventional excitation circuit detection device, Fig. 3 is an internal circuit diagram of a wound induction machine, and Fig. 4 5 is a conceptual diagram showing an embodiment of the present invention, FIG. 6 is a principle diagram of a current amplitude measuring device, and FIG. 7 is a principle diagram of another current amplitude measuring device. Fig. 8 is a current explanatory diagram in a steady state, Fig. 9 is a current explanatory diagram in a transient normal state, Fig. 10 is a current explanatory diagram when an excitation circuit is short-circuited, and Fig. 11 is another embodiment of the present invention. FIG. 12 is a circuit diagram of still another embodiment of the present invention, and FIG. 13 is a conceptual diagram of still another embodiment of the present invention. 1...Wound induction machine, 7...Exciting circuit short circuit detection device, Country 2) JA4 Mouth 9 Figures l Prisoner 8 Figure $ 11) I! 1 Vllll day kite 12 sword

Claims (1)

[Claims] 1. means for measuring the amplitude of the primary current or primary output of the wound induction machine; means for detecting periodic vibrations of the amplitude or output of the primary current; An excitation circuit short circuit detection device that detects a short circuit in an excitation circuit by repeating a predetermined number of circuits or more within a predetermined time. 2. An excitation circuit short circuit according to claim 1, characterized in that the time period for detecting the periodic pulsation is set to a period corresponding to twice the slip frequency of the wound induction machine. Detection device. 3. In claim 1, means for generating a signal with a frequency twice the slip frequency;
An excitation circuit short-circuit detection device, characterized in that periodic pulsation is detected by multiplication and integration with the current amplitude or output.