JPH0487177A - Severance sensing method for delta wiring three-phase load electric heater - Google Patents

Abstract

PURPOSE:To simplify the configuration by installing one current transformer on two of the phases connected to a three-phase power supply, allowing the positively directed current to flow in one phase of this current transformer, permitting the inverted direction current to flow in the other phase, sensing the change in the current difference between the two phases, and knowing wire severance which might be generated in either phase. CONSTITUTION:One current transformer 12 is installed on two of the three phases connected with a three-phase power supply 11, and a positively directed current is allowed to flow in one phase of this current transformer 12 while the inverted direction current is flowed in the other phase, and wire severance generated in either phase is known by sensing change in the current difference between the two phases. That is, an R-phase current 1a is flowed in positive direction in one current transformer 12 of penetration type while the T-phase current Ic is flowed oppositely, and thereupon vector calculation is conducted, and the secondary current obtained is fed to a temp. adjust meter 1 equipped with alarm for heater severance. With this type of current transformer 12 it is possible to sense wire severance in either phase of a three-phase electric heater 10. This decreases the number of current transformers 12 required to sense wire severance, and the configuration can be simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention (Industrial Field of Application) The present invention is directed to a three-phase load electric heater connected to a three-phase power supply, in which a disconnection occurs in any one of the three phases. The present invention relates to a method for detecting a disconnection in a Δ-connection three-phase load electric heater, in which the occurrence of a disconnection can be detected using a single current transformer.

(Prior Art) FIG. 4 shows a block diagram of a conventional temperature controller with a heater burnout alarm. The temperature controller 1 with heater breakage alarm detects the heating temperature by the electric heater 3 using the temperature sensor 2,
When controlling the temperature to approach the target temperature, the current transformer 4 detects the current from the single-phase power supply 5 flowing to the electric heater 3, and when this current is smaller than the appropriate value for the capacity of the electric heater 3, the heater 3 It determines that the wire is disconnected and issues an alarm, and at the same time, the relay 6 opens the connection circuit to the single-phase power supply 5. Therefore, the current transformer 4 can predict the occurrence of a break in the electric heater 3 before the temperature drops below the target temperature, thereby avoiding the production of defective products. can.

(Problems to be Solved by the Invention) However, in the temperature controller 1 shown in FIG. 4, the heater 3 is a single-phase load. In the case of a three-phase load, as shown in FIG.
When connecting the two line current detection current transformers 8 and 9 provided in the R phase and T phase, and the temperature controller 1 connected to the current transformers 8 and 9, A three-phase heater disconnection alarm 7 was required. For this reason, its configuration has become complicated, wiring work has increased, and costs have increased, hindering its widespread use.

In view of the above-mentioned points, an object of the present invention is to effectively solve the problems of the prior art, reduce the number of current transformers required for detecting a disconnection in a three-phase electric heater, and To provide a method for detecting disconnection in a Δ-connection three-phase load electric heater, which is reliable in detection, has a simplified configuration, has simple wiring, and is easy to handle.

[Structure of the Invention (Means for Solving the Problems)] In order to achieve the above object, the present invention provides a △-connection three-phase load electric heater connected to a three-phase power source. By detecting the change in the current difference between the two phases with one phase of one current transformer installed in two of the phases in the positive current direction and the other phase in the reverse current direction, the △ connection 3 is detected. This is a method for detecting a disconnection in a three-phase load electric heater with a Δ connection, which is characterized by detecting that a disconnection has occurred in any phase of the phase load electric heater.

(Function) By adopting the disconnection detection method of the △ connection type three-phase load electric heater of the present invention, one phase of one current transformer provided in two phases of the three phases connected to the three-phase power supply By detecting the change in the current difference between the two phases with the phase as the positive current direction and the other phase as the reverse current direction, a disconnection occurring in any phase of the Δ-connection three-phase load electric heater can be reliably detected, Its structure is simplified, its wiring is simplified, and its handling is easy.

(Example) Next, an example of the present invention will be described in detail based on the drawings.

FIG. 1 shows a schematic configuration diagram of an embodiment of the present invention.

In the figures, parts having the same functions as those in FIGS. 4 and 5 are given the same reference numerals. The R-phase current Ia is passed in the positive direction through one feedthrough current transformer 12, and the T-phase current 1c is
By flowing in the opposite direction, vector calculation is performed and the secondary current is supplied to the temperature controller 1 with a heater burnout alarm.

With such a current transformer 12, a three-phase three-wire balanced power supply 1
In a state where the three-phase electric heater 1o with a Δ wire connection load is connected to the three-phase electric heater 1o, it is possible to detect a disconnection of any phase of the three-phase electric heater 1o. The reason for this will be explained next.

FIG. 2 shows a connection state diagram of a three-phase electric heater, which is a Δ-connection load, to a three-phase three-wire balanced power supply.

Each current Ea, Eb, and Ec of a three-phase three-wire balanced power supply is calculated by the following formula (
1).

Ea-E, a E b-E a f-(1/2) -j (fco/
'l 1Ec-Ea(-(1/2) +j (f)
2) Eal-IEbl= 1Ecl
-(1) Also, Ea=RBiIB^, IB^-E a/RB
A-(2) Eb-RCB-ICB, ICB
-Eb/RCB・-(3)E c-RAC・ ■ ＾
C, I AC-E c/RAC... (4) Line current 1 a, I b, I c are expressed by the following formula (5), (8
), (7).

I a-I BA-I AC-(E a/RBA)-(
E c/RAC) = (E a/RBA) - (E a/R
AC)lI-(1/2)+(jJ'T/2))
...(5) I b-I CE-I BA
-(E b/RCB)-(E a/RBA)-<E a
/RCB)・f-(1/2)-j(JT/2)1-(E
a/RBA) -(6)Ic-
I AC-J CB-(E c/RAC)-(E b/
RCB)-(Ea/RAC)i-(1/2)"(j
JT72)i(Ea/RCB) ・I-(1/2)
-j(JT/2)1...(7) By the way, when detecting a change in line current at one location, for example, in the method of measuring line current 1a, as is clear from equation (5), the resistance If RB^, RAC changes, the line current becomes 1
a changes, but since there is no resistance RCB item, the resistance R
A change in CB does not result in a change in line current Ia. Therefore, it is impossible to detect changes in resistance RCB. Similarly, in the method of measuring line current Ib, resistance RA
Detection of changes in C is not possible. Furthermore, with the method of measuring the line current 1c, it is impossible to detect a change in the resistance RBA using equation (7).

Furthermore, when detecting a change in the sum of line currents at two locations, for example, the sum of line currents 1a+Ic can be calculated using equation (5) and (
From equation 7), the following equation (8) holds true.

I a+I c-(Ea/RB^)-(E a/R
AC)・f−(1/2) +j (JT/2)l+(
E a/RAC)・f-(1/2)+j (~/T/2
)-(E a/RCB) f-(1/2)-j(JT/2
)1-(E a/RBA)-(E a/RCB)・f
-(1/2)j(,/T72))
...(8) This equation (8) does not include an item for resistance RAC. Therefore, for a change in resistance RAC, the sum of line currents 1a+
Since Ic does not change, it is impossible to detect changes in resistance RAC. Similarly, if the sum of line currents is ia+1b or Ib+Ic, it is impossible to detect a change in resistance RBA or RCB.

However, when detecting a change in the difference between the line currents at two locations, for example, the following equation (9) holds true for the line current difference 1a-1c from equations (5) and (7).

I a-1c-(E a/RBA)-(E a/RAC
) ・I-(1/2) ”j(JT/2)l-(E a
/RAC)・f-(1/2)+j (V/T'/2))
-(E a/RCB)l-(1/2)-j(JT/2)
1-(Ea/RBA)-(Ea/RAC)I-1+j
a)+E a/RCB)・(-(1/2)-j(v'
T72)l ・++ (9) Equation (9) has items for each load resistance RB^, RAC, and RCB, so even if any of the load resistances RBA, RAC, and RC13 changes, the difference in line current 1a -1c changes. Therefore, the line current difference 1adC changes due to a change in the load resistances RBA, RAC, and RCB, that is, the occurrence of a disconnection, which can be detected. Note that the line current difference 1a-1b or I
The same is possible in the case of b-1c.

Therefore, as shown in FIG. 3, the line current 1a is caused to flow in the forward direction through one current transformer 12, and the line current 1c is caused to flow in the opposite direction by changing its direction, so that the negative side current 1a, I c
The secondary current i is subtracted by the magnetic flux generated, and the change in the current difference between the two phases is detected. Conventionally, at least two current transformers are required for detection, but one current transformer 12 is sufficient.

[Effects of the Invention] As explained above, the disconnection detection method of a △-connected three-phase load electric heater of the present invention uses one current transformer provided in two of the three phases connected to a three-phase power supply. The problems of the prior art are effectively solved by detecting changes in the current difference between the two phases with one phase in the positive current direction and the other phase in the reverse current direction.
It is possible to reliably detect a disconnection occurring in any phase of the Δ-connection three-phase load electric heater, simplify its configuration, simplify its wiring, and facilitate its handling.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram of an embodiment of the present invention, Fig. 2 is a connection state diagram of a 3-phase electric heater with a △ wire connection load to a 3-phase 3-wire balanced power supply, and Fig. 3 is the measurement principle in Fig. 1. Figure 4 is a connection state diagram of a temperature controller with a heater burnout alarm used in a conventional single-phase heater, and Figure 5 is a temperature controller with a heater burnout alarm used in a conventional △ wire connection load three-phase electric heater. FIG. 3 is a connection state diagram of the meter. 1...Temperature controller with heater burnout alarm 10...3-phase electric heater 11...3-phase 3-wire balanced power supply 12...Current transformer Attorney Patent attorney Hidekazu Miyoshi Figure 2 j3 Figure @ Figure 4 Figure 5

Claims (1)

[Claims] 1) In a delta-connected three-phase load electric heater connected to a three-phase power supply, one current transformer installed in two of the three phases connected to the three-phase power supply has one phase in the positive current direction. , the occurrence of a disconnection in any phase of the Δ-connection three-phase load electric heater is detected by detecting a change in the current difference between the two phases with the other phase in the reverse current direction. A method for detecting disconnection in a three-phase load electric heater.