JPS5926173B2 - Overcurrent relay for capacitor bank - Google Patents

Description

Detailed Description of the Invention The present invention electrically detects the melting of a capacitor unit fuse, and when the terminal voltage of the remaining healthy capacitor unit exceeds the allowable voltage due to overcurrent, the capacitor provides a tripping signal. This invention relates to overcurrent relays for banks.

In a capacitor bank consisting of multiple single-phase capacitors each connected to a fuse that will blow out in the event of an internal failure, the method of using a discharge type with all fuse displays and checking the blown state through visual inspection is more common than in the past. Although it is in practical use, the melting of the fuse is detected electrically,
It is not practical to protect the remaining healthy capacitor units.

The present invention seeks to provide an overall overcurrent relay for a capacitor bank which eliminates the above-mentioned drawbacks.

First, as shown in Figure 1, in a capacitor bank where multiple units of capacitors with fuses are assembled and connected in a double star shape, - n units are connected in parallel, and the unit capacity of one capacitor is When a short circuit occurs, three times the normal line current (rated current of the capacitor bank) flows through the faulty capacitor due to the short circuit, blowing the fuse, but during the time it takes for the fuse to completely blow, the same current flows at the neutral point. flows.

Next, after the fuse blows, the following overvoltages will be applied to the remaining healthy capacitors in the fault phase.

In other words, when a capacitor bank is constructed by connecting kn capacitors with fuses in parallel as shown in Figure 1, the combined capacitance kcr in a healthy state is 1.
If the combined capacitance c2 when the fuse of one unit is blown is the capacitance kc of one capacitor, then C1-n
From C, it changes to c2=(n-1)c.

In FIG. 1, if a short-circuit accident occurs in the capacitor on the left side of the U phase (on the neutral point N side), the calculation will be as follows.

In Fig. 1 and Fig. 4, the voltage V between neutral point N-N'
N (open between neutral point N-N') is neutral point N-N
'The impedance Co seen from
'+ l l '''''2 Neutral point current IN is here I = jωCIE (current responsible for line current in normal condition) C
=nCC2-(n-1) By substituting C, a fault occurs and the current Iu flowing through the fault phase (C2+C1) is determined.

In the circuit shown in FIG. 4, the neutral point voltage W becomes.

The line current I' on the C2 side where the accident occurred is: Therefore, the current (■) per healthy capacitor becomes an overcurrent, that is, an overvoltage, by α compared to the current before the accident.

If one more fuse blows in the same phase, the neutral point current I N/ becomes:

The progression of this accident is illustrated in Figure 2.

The horizontal axis shows time, the vertical axis shows neutral point current IN, ■ shows the line current in a normal state, and Is shows the setting value of an overcurrent relay, which will be described later.

Next, the operation of the overcurrent relay for a capacitor bank according to the present invention will be explained with reference to FIG.

Terminals T and T6 are connected to the secondary side of the current transformer 3 for neutral point current detection.

The main contact 7 is a contact that operates when the main coil 4 is excited by a neutral point current, and has a time-limiting characteristic.

The instantaneous contact 6 is a contact that closes when the instantaneous coil 5 is excited, and its operating value is such that it instantaneously closes when the aforementioned fault current 3I flows.

When a short-circuit failure occurs in a single capacitor, a current of 3 cm flows between the capacitor and the neutral point, causing the fuse to start blowing.

If the breaker is tripped by the neutral point current flowing at this time, the fuse will not blow, but in the overcurrent relay for capacitor banks of the present invention, the instantaneous contact 6 closes first and shorts the main coil 4, so the main coil 4 is short-circuited. Since the contact 7 does not close and no tripping signal is generated, the fuse is reliably blown.

After the fuse blows, the neutral point current is reduced to the current shown in equation (1), so the instantaneous contact 6 is opened and the main coil 4
is excited.

As the accident progresses, when the neutral point current shown by equation (4) exceeds the set value of this capacitor bank overcurrent relay, a trip signal is issued to protect the remaining healthy capacitors.

Generally, the setting value of the above-mentioned overcurrent relay for a capacitor bank is a factor of 10 or less of the rated current of the capacitor bank, and the operating value of the instantaneous contact 6 is a factor of 200 or more, so that non-operation is ensured.

The terminals T and T4 are closed by instantaneous contacts 6, so that the operation of the fuse can be output as a signal to the outside, and the auxiliary coil 8 is used to indicate the operation of the overcurrent relay for the capacitor bank. It is something.

T and T2 are terminals.

As described above, according to the present invention, it is possible to detect a failure in a single capacitor in a capacitor bank with a fuse, which was not considered in the past, and it is possible to completely protect the remaining healthy capacitors from being affected by the accident. It is economically effective and has great industrial and practical value.

[Brief explanation of drawings]

Figure 1a shows a collection of multiple capacitors with fuses,
A connection diagram of a capacitor bank connected in a double star configuration, Figure 1 is a detailed connection diagram for one phase of Figure 1a, Figure 2 is a time chart showing the progression of the accident, and Figure 3 is a capacitor of the present invention. FIG. 4 is an internal connection diagram of the bank overcurrent relay, and is an explanatory diagram in a three-phase AC circuit. 1 Ni fuse, 2: Single capacitor, 1' 2 I fuse connected to single capacitor 2' where fault occurred, 2': Single capacitor where fault occurred, 31 Current transformer for neutral point current detection, 4
: Main coil, 5: Instantaneous coil, 6: Instantaneous contact, 7 Two main contacts, 8: Auxiliary contact.

Claims (1)

[Claims] 1. Detects the neutral point current of a capacitor bank configured with multiple capacitors connected in series with fuses in a double star configuration, and in the event of an internal failure in the above capacitor, operates after the fuse blows out, and the remaining healthy capacitors This is an overcurrent relay for a capacitor bank that protects a unit from overvoltage.In series with the main coil that drives a contact that operates for a limited time to give a trip signal to the outside, an instantaneous contact that operates instantaneously with an overcurrent is connected. An overcurrent relay for a capacitor bank, comprising a coil, and the instantaneous contact is connected in parallel to the main coil.