JPS6117216B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for protecting a power distribution system having a current limiting reactor, and particularly to a protection system for saving power.

Conventionally, current-limiting reactors have been used to limit short-circuit current in the event of a failure. However, although the current limiting reactor is unnecessary except in the event of a failure, in the conventional system it is always connected to the grid, so wasted power is consumed in the current limiting reactor.

An example of such a power distribution system is shown in FIG. In Figure 1, L is the current limiting reactor, CBI is the primary side breaker of the current limiting reactor L, OTI is the current transformer of the CBI system, OCI is the overcurrent relay that protects the CBI system from overload and short circuit accidents, CBF is a breaker on the secondary side of the current limiting reactor L, CTF is a current transformer on the distribution line, and OCF is an overcurrent relay that protects the distribution line from overloads and short circuits. Although there are generally several distribution lines, only one system is shown as a representative.

Further, point A is a short-circuit point on the distribution line, point B is a short-circuit point on the common bus of the distribution line, and point C is a short-circuit point on the primary side of the reactor. First, we will discuss conventional protection methods for such power distribution systems.

If there is a short circuit accident at point A, it will operate with a short circuit.
The CBF is tripped by the instantaneous element OCF-INST of the OCF. In this case, the instantaneous element OCI-INST of OCT
also works, but generally OCI-INST is OCF-INST
In order to maintain short-circuit coordination with the CBI, a time-limited relay is used to trip the CBI after a certain period of time, providing backup protection.

If a short circuit occurs at point B, OCI-INST will operate and CBI will be tripped after the specified time period. In the case of a short circuit accident at point C, the same protection as at point B is provided. An example of the operating characteristic curve of an overcurrent relay in such a protection system is shown in FIG. If is the rated current of the CBF system, IiI is the rated current of the CB system, and Ist2 is the primary side short-circuit current of the current limiting reactor L. OCF-CL and OCI-OL are long-term characteristic curves that operate under overload, and are generally set to operate at around 150% of the rated current. Also, OCF-INST is A
This is an instantaneous element that operates with a point short circuit, and is set to a current value below Ist2. Furthermore, OCI-INST is A, B, C
It is an instantaneous element that operates as a point short circuit, and in order to coordinate protection with OCF-INST in the event of a short circuit at point A, the CBF trip time T (usually 0.2~
The CBI is then tripped after a delay of 0.3 seconds).

Next, an example of the power consumption of the current limiting reactor is calculated from the rated value as follows. The capacity of current limiting reactor L is 40MVA, the % impedance is 4%,
If the primary side voltage of the current limiting reactor L is 10K.V, the voltage drop e of the current limiting reactor is becomes. Also, the rated current of current limiting reactor L is The power consumption when the rated current flows through the current limiting reactor L is the apparent power: √3×0.231kv×2310A=924KVA. In other words, in conventional power distribution systems,
924KVA is consumed.

As described above, in the conventional method, when a short circuit occurs at point B or point C, there is a certain time delay, which aggravates the short circuit and wastes energy.

The present invention has been made in consideration of the above-mentioned drawbacks and provides an economical method of protecting a power distribution system that can save the power consumed by the current limiting reactor during normal operation.

The present invention will be explained below based on an embodiment shown in FIG.

In Figure 3, the current limiting reactor L in Figure 1 is
In addition, in place of the OCI shown in Fig. 1, a long-time characteristic element OCI ₂ which operates in the event of an overload is connected in parallel with the breaker CBL having the same rating as the _CBI. - INST and rated current of 200
The second instantaneous element OCI ₂ operating in the range ~400% -
Overcurrent relay OCI ₂ with HDO is used.

The second instantaneous element OCI ₂ of this overcurrent relay OCI ₂
- HDO is used to protect motors with important loads.
For example, if you want to force the electric motor to operate due to the nature of the load, such as a water pump in a thermal power plant, High Drap
Used as a cut. Furthermore, this HDO has a high ratio of return current to operating current.

FIG. 4 shows an example of an operating characteristic curve when such an overcurrent relay OCI ₂ is used. OCI ₂ -OL
is a long-time element that operates with overload, OCI ₂ -HDO is a second instantaneous element that operates with 200-400% of the rated current, and OCI ₂ -INST is a first instantaneous element that operates with short circuit. Generally OCI ₂ - OL is 150% of rated current
OCI ₂ - INST is set to operate at 400% due to instantaneous operation, taking into account system inrush current, etc.
It is often set at a higher value. Therefore OCI ₂ -
OL and OCI ₂ - INST section from 200 to 400 of rated current
The second instantaneous element OCI ₂ - HDO, which operates at
It is possible to trip the shield breaker CBL more quickly and insert the current limiting reactor L into the system. Shiya disconnector
CBL systems are generally power receiving systems, so if the power receiving system is overloaded by 200 to 400%, it means that all the lower distribution lines are overloaded, or when one distribution line is overloaded, the electric power of the other system is overloaded. There are many special cases such as the influence of the starting current. Generally, there are 200 to 400 power receiving systems.
In the case of % overload, it often turns into a short circuit, so it is preferable to trip the shield breaker CBL using the OCI ₂ -HDO. In addition, if OCI ₂ - HDO operates but the first instantaneous element OCI ₂ - INST does not operate, confirm that the overcurrent relay OCF on the distribution line is not operating and automatically turn on the breaker CBL. Therefore, there is no problem even if the line breaker CBI does not transition from overload to short circuit.

Next, the operation of the present invention will be explained in more detail with reference to the flowcharts shown in FIGS. 5A and 5B.

Furthermore, OCF-OL, OCF-INST, OCI ₂ -OL,
OCI ₂ - HDO, OCI ₂ - INST automatically recovers when the fault point is isolated. When a failure occurs, the protection method is to determine whether the failure point is point A, point B, or point C.
It varies depending on the point. Now, in the case of a failure at point A, first OCF-INST, OCI ₂ - HDC or OCI ₂ -
Check if INST is not running. OCF―
If INST is not operating, check if OCF-OL is not operating. If it is operating, there is an overload accident on the distribution line, so trip the CBF and complete the protection. Also OCF-INST, OCI ₂ -HDO, OCI ₂
- If any INST is operating, it is considered a short circuit and the CBL is tripped and the current limiting reactor L is placed in the system.
Insert. After CBL is tripped, CBF is tripped to provide short circuit protection at point A. Since the distribution line at point A is disconnected by tripping the CBF, OCF-OL
Alternatively, OCF-INST will recover and automatically turn on the CBL again when it becomes inactive. If a short circuit occurs
If CBL and CBF are not tripped, CBI is tripped as backup protection to complete failure protection at point A.

Next, when a failure occurs at points B and C, see Figure 5 B.
Go to OCI ₂ - If OL is operating, it is overloaded, so trip CBI and end protection.
Also OCI ₂ -OL is not working and OCI ₂ -HDO
If the CBL is operating, there is a possibility of an overload of 200% or more of the rated current or a short circuit, so first trip the CBL. OCI ₂ - HDO after CBL trip is completed
If the OCI 2-INST returns, check that the OCI ₂ -INST is not working, go to A in Figure 5, and then check the OCF.
- If OL or OCF-INST is not working, it means that the fault has disappeared and CBL is automatically turned on again. Also, if CBL is not tripped even if OCI ₂ - HDO operates, CBI is tripped to protect it. B
If OCI ₂ - INST operates due to a failure at point and point C, it is a short circuit and CBI and CBL are instantly tripped.

By doing the above, it is possible to detect signs of a short circuit using OCI ₂ - HDO and insert the current limiting reactor L into the system at an early stage, so that protection can be ensured within the short circuit withstand time of the switchboard, and furthermore, the current limiting reactor L can be inserted at an early stage. There is no loss in reactor L.

Next, FIGS. 6 and 7 are system diagrams showing other embodiments of the present invention, respectively.

Figure 6 is an example of a power distribution system when the contact distance between the power transmission side and the power receiving side is long, and the shingle breaker CBR and overcurrent relay OCR are connected in series with the shingle breaker CBI and overcurrent relay OCI ₂ . This is the case. In such a case, OCI ₂ can be used to remove the CBI and at the same time
CBR can also have a similar effect by tripping.

Moreover, FIG. 7 shows a case where a current limiting reactor is installed on the power transmission side when the connection distance between the power transmission side and the power reception side is long. In such a case, a similar effect will be applied to the power transmission side system, and the overcurrent relay OCP will not trip the shield cutter CBP on the power receiving side. In other words, the same effect can be achieved by treating the disconnector CBP as a disconnector.

As explained above, according to the present invention, it is possible to obtain a rational protection method for a power distribution system that saves power consumption of a current limiting reactor and performs an effective protection operation.

[Brief explanation of the drawing]

Fig. 1 is a system diagram showing a conventional power distribution system protection method, Fig. 2 is a diagram showing the protection coordination curve of Fig. 1, Fig. 3 is a system diagram showing an embodiment of the present invention, and Fig. 4 is a system diagram showing the protection coordination curve of Fig. 1. FIG. 3 is a diagram showing a protection coordination curve, FIGS. 5A and 5B are flowcharts showing the operation of the present invention, and FIGS. 6 and 7 are system diagrams showing other embodiments of the present invention, respectively. CBI, CBL, CBF...Shipping breaker, L...Current limiting reactor, OCI ₂ , OCF...Overcurrent relay, OCI ₂ - OL
...Anti-time element, OCI ₂ , HDO...Second instantaneous element,
OCI ₂ - INST...first instantaneous element, CTI, CTF,
CTP, CTR...Current transformer.

Claims (1)

[Claims] 1. In a distribution system in which the distribution bus is connected to the power supply system through a current limiting reactor and a shingle breaker, and the load is connected from the distribution bus through the shingle breaker, the current limiting reactor and shingle breaker are connected to the power supply system. In addition to connecting in parallel, on the primary side of the current limiting reactor, there is a counter-time element that responds to overload current, a first instantaneous element that responds to short-circuit current, and a second instantaneous element that operates at 200 to 400% of the rated load current. An overcurrent relay is provided, and under normal conditions, current is supplied to the distribution bus by bypassing the current limiting reactor via the parallel shunt, and when the first instantaneous element or the second instantaneous element is activated. First, the parallel breaker is tripped, and then the corresponding breaker protection operation is performed, and when the breaker protection operation is completed and the fault is removed, the parallel breaker is tripped. A method for protecting a power distribution system characterized by automatically turning on the power.