An overload relay latching control method and system

Abstract

This invention discloses an overload relay interlocking control method and system, belonging to the field of power equipment protection and control. The method includes multi-source signal acquisition, automatic matching of operating modes, interlocking logic judgment and execution, interlocking reset judgment and execution steps. It acquires the load current signal of the power equipment and the switch position signal characterizing its operating mode. Based on the switch position signal, it automatically matches the corresponding operating mode and interlocking parameters, compares the effective current value with the interlocking threshold, and executes the interlocking operation. The interlocking is released when the reset condition is met. The supporting system includes a signal acquisition layer, a transmission layer, a main control layer, an execution layer, and a human-machine interface layer. These layers work together to implement the above control process. This invention can adapt to different power equipment operating modes, reduce signal interference, avoid equipment overload damage, maintain stable acquisition and judgment functions, and also supports flexible intervention under special operating conditions for convenient operation and maintenance. It can achieve reliable overload protection for power equipment in multiple scenarios.

Description

Technical Field

[0001] This invention relates to the field of power equipment protection and control, and in particular to an overload relay interlocking control method and system. Background Technology

[0002] Currently, power equipment (such as substation main transformers and industrial plant fans) is a core component of power systems and industrial production, and its stable operation directly affects the reliability of power grid supply and production efficiency. With the expansion of power system capacity and the increasing automation of industrial production, overload relays, as key protection devices to prevent overload damage to power equipment, are widely used in various power equipment operation and control scenarios. The industry generally requires overload relays to possess basic functions such as signal acquisition, mode adaptation, interlocking protection, and automatic reset to meet the protection needs of equipment under different operating modes (such as parallel operation and split operation), while also ensuring the stability of signal transmission and the timeliness of protection actions, thus providing support for the safe operation of power equipment.

[0003] Existing overload relay interlocking control technology still has technical problems that are not compatible with actual application needs: First, existing control methods mostly only collect a single load current signal and do not simultaneously collect switch position signals that characterize the equipment's operating mode, making it impossible to formulate targeted protection strategies based on the actual operating status of the equipment; Second, there is a lack of an automatic matching mechanism for operating modes based on switch position signals, requiring manual preset or switching of interlocking parameters, which is difficult to adapt to scenarios with dynamic changes in equipment operating modes and has insufficient adaptability; Third, the interlocking logic judgment does not form a complete linkage process of "current effective value calculation and comparison - action delay timing - interlocking signal output", which is prone to false triggering or response delay due to incomplete judgment logic; Fourth, the interlocking reset judgment does not combine the interlocking threshold and reset ratio for accurate judgment, making it impossible to reliably release the interlock when the equipment load falls back to a safe range, either resetting too early, causing the equipment to still face the risk of overload, or resetting too late, affecting the normal operation and recovery of the equipment. Summary of the Invention

[0004] The purpose of this invention is to overcome one or more shortcomings of the prior art and provide an overload relay lockout control method and system.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] An overload relay lockout control method includes the following steps:

[0007] Step 1). Multi-source signal acquisition: Acquire the load current signal of the power equipment, and at the same time acquire the switch position signal that characterizes the operating mode of the equipment;

[0008] Step 2). Automatic matching of operating modes: Preset the interlocking parameters corresponding to two operating modes. The interlocking parameters include the interlocking threshold, action delay time and reset ratio. Automatically match the corresponding operating mode and the interlocking parameters in the mode according to the collected switch position signal.

[0009] Step 3). Interlocking logic judgment and execution: The effective value of the current calculated from the collected load current signal is compared with the interlocking threshold in the current operating mode. If the effective value of the current is ≥ the interlocking threshold, the action delay timer is started. When the timer reaches the preset action delay time, the control relay outputs an interlocking signal to forcibly interrupt the target control operation of the power equipment.

[0010] Step 4). Lockout reset judgment and execution: If the effective value of the current is less than the lockout threshold, then it is further judged whether the effective value of the current is less than or equal to the product of the lockout threshold and the reset ratio. If so, the reset delay timer is started. After the timer ends, the relay is controlled to reset and the lockout is released.

[0011] Furthermore, the process of acquiring the load current signal in step 1) includes: sampling the load current at a sampling rate of not less than 32 points / 20ms, and calculating the effective value of the current through the root mean square value algorithm; the acquisition range of the load current signal is 0~6A, the rated acquisition current is 5A, and the acquisition accuracy is ≤0.5%.

[0012] Furthermore, the process of acquiring the switch position signal in step 1) includes: acquiring the switch position signal through either wireless transmission or fiber optic transmission, and transmitting the acquired switch position signal to the subsequent judgment stage after processing by the isolation module; the isolation module has an isolation withstand voltage ≥500Vp-p to avoid signal distortion caused by external electromagnetic interference.

[0013] Furthermore, it also includes a manual mode switching step: when manual intervention is required, the system switches to manual mode through human-computer interaction, and manually inputs the locking threshold, action delay time and reversion ratio for different operating modes. Subsequent locking logic judgment and execution, as well as locking reversion judgment and execution, are all based on the manually input parameters.

[0014] Furthermore, the process of controlling the relay output lockout signal in step 3) includes: controlling the operation of two independent sets of relay contacts, each set of relay contacts including one normally open contact and one normally closed contact. After the operation, the normally open contact closes and the normally closed contact opens. The contact capacity of the relay contacts meets the switching requirements of 2A / 250VAC and 2A / 30VDC, and supports maintaining the operating state for a long time.

[0015] Furthermore, in step 1), the two preset operating modes are parallel operating mode and split operating mode: the blocking threshold in parallel operating mode is 85% of the rated current of the power equipment, and the blocking threshold in split operating mode is 100% of the rated current of the power equipment; the reset ratio in both operating modes is preset to 20%.

[0016] Furthermore, it also includes abnormal current withstand handling steps: when the collected load current reaches twice the rated collected current, the collection and judgment functions are maintained without damage for 1 hour; when the collected load current reaches 20 times the rated collected current, the collection and judgment functions are maintained without damage for 1 second.

[0017] An overload relay interlocking control system includes a signal acquisition layer, a transmission layer, a main control layer, an execution layer, and a human-machine interaction layer that work in sequence and in coordination. The specific working steps are as follows:

[0018] Signal acquisition layer: The load current signal is acquired through the current acquisition submodule, and the switch position signal is acquired through the switch position acquisition submodule;

[0019] Transmission layer: The switch position signal acquired by the switch position acquisition submodule is transmitted to the main control layer through the wireless transmission submodule or the fiber optic transmission submodule;

[0020] Main control layer: Receives load current signal transmitted from signal acquisition layer and calculates effective current value; receives switch position signal transmitted from transmission layer and matches operating mode and interlocking parameters; executes interlocking logic judgment and reset judgment.

[0021] Execution layer: Receives control commands from the main control layer and drives relays to output interlock or reset signals;

[0022] Human-machine interaction layer: Displays the current switch position status, current effective value and lockout status, and provides operation interfaces for parameter setting and mode switching.

[0023] Furthermore, the working process of the signal acquisition layer in step 1) includes:

[0024] The current acquisition submodule connects to the load current through a non-polar current input terminal. The current signal is converted into a digital signal by a high-precision AD chip and then transmitted to the main control layer. The high-precision AD chip is a ΔΣ type AD chip, which is used to ensure the accuracy of current acquisition.

[0025] The switch position acquisition submodule receives the switch position no-contact signal through the switch position signal terminal, and transmits it to the transmission layer after being processed by the optocoupler isolation circuit. The optocoupler isolation circuit is used to achieve electrical isolation between the switch position signal and the internal circuit of the system.

[0026] Furthermore, the main control layer's operation in step 3) includes: calculating the effective value of the current by executing the root mean square value algorithm through the main control chip, pre-setting a database of interlocking parameters for two operating modes, and calling the corresponding parameters according to the switch position signal; the wireless transmission submodule of the transmission layer operates in the 2.4~2.5GHz ISM band, and the optical fiber transmission submodule supports parsing the location messages output by the power equipment intelligent terminal; the relay drive circuit of the execution layer converts the level signal output by the main control chip into a relay coil drive current through a transistor, driving the relay contacts to operate, and the drive circuit is equipped with a freewheeling diode to prevent the reverse electromotive force when the relay is disconnected from breaking down the transistor.

[0027] The beneficial effects of this invention are:

[0028] (1) By using multi-source signal acquisition and automatic matching technology for operating modes, the system can adapt to different power equipment operating modes, reduce signal interference, and ensure data reliability.

[0029] (2) By using the interlocking logic judgment execution and abnormal current withstand technology, the effect of avoiding equipment overload damage and maintaining the stability of the acquisition and judgment function can be achieved;

[0030] (3) Through manual mode switching and human-computer interaction technology, the effect of flexible intervention in special working conditions and convenient monitoring of equipment status by operation and maintenance personnel can be achieved. Attached Figure Description

[0031] Figure 1 Diagram showing the working relationship between overload relay signal acquisition and interlocking control in the main transformer voltage regulation system;

[0032] Figure 2 Business structure diagram of overload relay in main transformer voltage regulation system;

[0033] Figure 3 This is a block diagram of the hardware structure of the overload relay in the wind turbine start-stop system.

[0034] Figure 4 Software flowchart for overload relay interlocking control logic and mode selection. Detailed Implementation

[0035] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Example 1: Overload relay interlocking control of the main transformer voltage regulation system:

[0037] This embodiment applies to a 110kV substation main transformer voltage regulation scenario, and the implementation process is as follows:

[0038] Step 1. Multi-source signal acquisition:

[0039] See Figure 1 Establish a signal acquisition link: the load current on the secondary side of the transformer is led out through the current transformer and connected to the intelligent terminal, and then transmitted to the load current measurement unit.

[0040] The "closed / open" status signal of the bus tie switch is output from its contacts to the contact signal wireless transmission device in the control cabinet, and the corresponding contact signal wireless receiving device is installed in the main transformer terminal box to realize remote transmission of position signals.

[0041] The load current is acquired using a 32-point / 20ms sampling rate. The effective value of the current is calculated using the root mean square algorithm. The acquisition range is set to 0~6A, the rated acquisition current is 5A, and the acquisition accuracy is ≤0.5% after debugging.

[0042] Both the load current signal and the bus tie switch position signal are processed by an isolation module with an isolation withstand voltage ≥500Vp-p to eliminate electromagnetic interference. The processed signals are then transmitted to the CPU module. If wireless transmission is obstructed, the system can switch to fiber optic transmission mode to receive position messages output by the bus tie switch intelligent terminal.

[0043] Step 2. Automatic matching of operating mode:

[0044] See Figure 2 The locking parameters for the two operating modes can be preset through the human-computer interaction interface shown in the figure:

[0045] Parallel operation mode (bus tie switch closed): blocking threshold is 85% of the main transformer's rated current (5A×85%=4.25A), action delay time is 1s, and reset ratio is 20%;

[0046] Separate operation mode (bus tie switch open): blocking threshold is 100% of the rated current of the main transformer (5A), action delay time is 2s, and reset ratio is 20%.

[0047] The CPU module receives the isolated bus tie switch position signal, automatically identifies the operating mode, and calls the corresponding parameters: "closed" signal calls the parallel mode parameters, and "open" signal calls the split mode parameters. Meanwhile, the switching power supply module in the diagram provides multiple adaptable voltages (+5V for the CPU, +9V for the current acquisition circuit, and +36V for the wireless receiver), supporting a wide input range of 220VAC / DC.

[0048] Step 3. Lockout logic judgment and execution:

[0049] The CPU module continuously receives the effective current value data and compares it with the blocking threshold of the current operating mode in real time: if the main transformer is in parallel operation and the effective current value rises to 4.5A (≥4.25A), a 1-second action delay timer is immediately started; if the current falls back below 4.25A during the timer, the timer is reset and monitoring resumes; if the current continues to meet the threshold condition and the timer is up to standard, the CPU module sends an action command to the relay output module in the figure.

[0050] The relay output module controls the synchronous operation of two independent sets of contacts: normally open contacts change from open to closed, and normally closed contacts change from closed to open; the contact capacity meets the switching requirements of 2A / 250VAC and 2A / 30VDC, and supports long-term maintenance of the operating state. The interlock signal is transmitted to the intelligent terminal. Figure 1 The on-load tap changer in the transformer is forcibly disconnected from the main transformer voltage regulation drive circuit, thus interrupting the on-load tap changer operation.

[0051] Step 4. Lockout Reset Judgment and Execution:

[0052] When the main transformer load decreases, and the CPU module detects that the effective value of the current drops to 0.8A (≤4.25A×20%), it starts a 2-second reset delay timer. During the timer, it continuously confirms that the current remains stable below the reset value. Once the condition is met and the timer ends, the CPU module sends a reset command.

[0053] The relay contacts return to their initial state, releasing the lockout on the on-load mechanism, and the main transformer resumes its normal voltage regulation function. During the reset process, the human-machine interface displays "current value - reset timer - lockout status" in real time. If manual intervention is required, the interface can be switched to manual mode to modify the lockout threshold and delay time; the parameter changes take effect immediately.

[0054] Example 2: Overload relay interlocking control of the fan start-stop system:

[0055] This embodiment is applied to the start-stop control scenario of high-power fans in industrial plants. It is implemented according to the following steps: "multi-source signal acquisition - automatic operation mode matching - interlocking logic judgment and execution - interlocking reset judgment and execution". The details are as follows:

[0056] S1. Multi-source signal acquisition:

[0057] See Figure 3 The relay's hardware core consists of a 16-bit Σ-Δ type AD chip, an isolation barrier, a CPU module, a relay output unit, and a switching power supply module, which completes signal input and processing according to hardware logic.

[0058] The load current of the wind turbine power supply circuit is led out through the secondary side of the current transformer and connected to the "input current" channel of the hardware structure; the control switch dry contact signal, which represents the wind turbine operating mode (parallel / individual), is connected to the "control dry contact input" terminal.

[0059] Both types of signals are first processed through an isolation barrier. The isolation barrier can block electromagnetic interference in the industrial field, prevent external signals from interfering with internal circuits, ensure signal transmission stability, and conform to the "input-isolation-core processing" link design in the hardware structure.

[0060] The isolated current signal is transmitted to a 16-bit Σ-Δ type AD chip, which performs the conversion from analog to digital signal. The converted digital current signal and the isolated switch position signal are then transmitted to the CPU module.

[0061] The CPU module performs preliminary processing on the current signal, such as filtering and RMS value calculation, to provide digital input that meets hardware requirements for subsequent logical judgments.

[0062] Meanwhile, the switching power supply module provides the appropriate operating voltage for the AD chip, isolation barrier, CPU module and relay output unit, ensuring that each hardware module operates collaboratively according to the structural logic.

[0063] S2. Automatic operation mode matching:

[0064] See Figure 4 For operation mode identification and parameter configuration:

[0065] After the relay is powered on, it first enters the initialization phase. The CPU module performs fault self-checks on the AD chip, isolation barrier, relay output unit and human-machine interface (including display components and operation buttons) in the hardware structure.

[0066] If a hardware module malfunctions, an alarm will be displayed through the human-machine interface; after the self-test passes, the system will enter the parameter configuration ready state.

[0067] By using the operation buttons on the human-machine interface, you can enter the parameter setting interface and preset the interlocking parameters (including interlocking threshold, action delay time, and reset ratio) for two fan operation modes (corresponding to the "closed / open" state of the control switch dry contact). The parameters are saved to the built-in storage unit of the CPU module, and the preset results are displayed on the interface for confirmation.

[0068] The system then enters the mode selection phase: if the drone is interactively operated, it automatically reads the isolated switch position signal, matches the corresponding operating mode according to the signal status, and calls the preset parameters.

[0069] If a manual operation command is detected, the operating mode and parameters can be set directly via buttons to adapt to the need for manual intervention under special working conditions.

[0070] S3. Lockout logic judgment and execution:

[0071] Coordinate hardware architecture and software flow to execute interlock control:

[0072] The CPU module controls the AD chip to continuously acquire the load current signal, calculates the effective value of the current, and then compares it with the blocking threshold of the current operating mode in real time.

[0073] If the effective value of the current reaches or exceeds the blocking threshold, the action delay timer is started, and the current is continuously collected during the timer.

[0074] If the current falls below the threshold, the timer is automatically reset and returns to continuous acquisition mode; if the current continues to meet the threshold condition and the timer reaches the preset time, the CPU module generates a latching instruction.

[0075] The latching command is transmitted to the relay output unit, which includes a relay drive circuit and two sets of independent relays (each set contains one normally open contact and one normally closed contact).

[0076] After receiving the instruction, the drive circuit converts the level signal output by the CPU into a relay coil drive current, driving two sets of relays to operate synchronously: the normally open contact changes from open to closed, and the normally closed contact changes from closed to open.

[0077] The relay contacts have the switching capacity to meet the requirements of industrial control circuits and can maintain the operating state for a long time, outputting a lockout signal according to hardware logic.

[0078] The interlock signal is transmitted to the fan control circuit through the output terminal, cutting off the fan start-stop drive circuit and forcibly interrupting the fan operation; at this time, the human-machine interface displays the current interlock status, prompting on-site personnel to pay attention to the equipment load.

[0079] S4. Lockout Regression Judgment and Execution:

[0080] By combining software regression logic with hardware response, system recovery can be achieved:

[0081] When the wind turbine load decreases and the effective value of the current collected by the CPU module drops below "blocking threshold × reset ratio", the reset delay timer is started; if the current rises back above the reset condition during the timer, the timer is immediately reset to zero and the data collection state is restarted.

[0082] If the current remains stable below the reset condition and the timing ends, the CPU module generates a reset instruction.

[0083] After the reset command is transmitted to the relay output unit, the drive circuit stops outputting current, the relay coil is de-energized, and the contacts return to their initial state (normally open contacts open, normally closed contacts close), thus releasing the lockout on the fan control circuit.

[0084] The human-machine interface is updated to the "lockout released" state, and the fan resumes normal start-stop function.

[0085] If the operating characteristics of the wind turbine are adjusted (such as changes in operating conditions after maintenance), the interlocking parameters can be readjusted through the human-machine interface. After the parameters are modified, they are immediately synchronized to the CPU module and automatically updated to subsequent stages to ensure that the system adapts to dynamic operating requirements.

[0086] In the above embodiments, the two overload relay interlocking control embodiments of the main transformer voltage regulation system and the wind turbine start-stop system both achieve the effects of adapting to different power equipment operation modes, reducing signal interference and ensuring data reliability through multi-source signal acquisition and automatic operation mode matching technology; they achieve the effects of avoiding equipment overload damage and maintaining stable acquisition and judgment functions through interlocking logic judgment execution and abnormal current withstand technology; and they achieve the effects of flexible intervention in special working conditions and convenient monitoring of equipment status by operation and maintenance personnel through manual mode switching and human-machine interaction technology, thus realizing reliable overload protection of power equipment in different scenarios.

[0087] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. An overload relay lockout control method, characterized in that, Includes the following steps: Step 1). Multi-source signal acquisition: Acquire the load current signal of the power equipment, and at the same time acquire the switch position signal that characterizes the operating mode of the equipment; Step 2). Automatic matching of operating modes: Preset the interlocking parameters corresponding to two operating modes. The interlocking parameters include the interlocking threshold, action delay time and reset ratio. Automatically match the corresponding operating mode and the interlocking parameters in the mode according to the collected switch position signal. Step 3). Interlocking logic judgment and execution: The effective value of the current calculated from the collected load current signal is compared with the interlocking threshold in the current operating mode. If the effective value of the current is ≥ the interlocking threshold, the action delay timer is started. When the timer reaches the preset action delay time, the control relay outputs an interlocking signal to forcibly interrupt the target control operation of the power equipment. Step 4). Lockout reset judgment and execution: If the effective value of the current is less than the lockout threshold, then it is further judged whether the effective value of the current is less than or equal to the product of the lockout threshold and the reset ratio. If so, the reset delay timer is started. After the timer expires, the relay is controlled to reset and the lockout is released. It also includes abnormal current withstand handling steps: when the collected load current reaches twice the rated collected current, the collection and judgment functions are maintained without damage for 1 hour; when the collected load current reaches 20 times the rated collected current, the collection and judgment functions are maintained without damage for 1 second. It also includes a manual mode switching step: when manual intervention is required, the system switches to manual mode through human-computer interaction, and manually inputs the locking threshold, action delay time and reversion ratio for different operating modes. Subsequent locking logic judgment and execution, as well as locking reversion judgment and execution, are all based on the manually input parameters.

2. The overload relay lockout control method according to claim 1, characterized in that, The process of acquiring the load current signal in step 1) includes: sampling the load current at a sampling rate of not less than 32 points / 20ms, and calculating the effective value of the current through the root mean square value algorithm; the acquisition range of the load current signal is 0~6A, the rated acquisition current is 5A, and the acquisition accuracy is ≤0.5%.

3. The overload relay lockout control method according to claim 1, characterized in that, Step 1) involves acquiring the switch position signal, which includes: acquiring the switch position signal through either wireless transmission or fiber optic transmission, and then transmitting the acquired switch position signal to the subsequent judgment stage after processing by an isolation module; the isolation module has an isolation withstand voltage of ≥500Vp-p to avoid signal distortion caused by external electromagnetic interference.

4. The overload relay lockout control method according to claim 1, characterized in that, Step 3) involves controlling the relay output lockout signal, which includes controlling two independent sets of relay contacts to operate. Each set of relay contacts includes one normally open contact and one normally closed contact. After operation, the normally open contact closes and the normally closed contact opens. The contact capacity of the relay contacts meets the switching requirements of 2A / 250VAC and 2A / 30VDC and supports maintaining the operating state for a long time.

5. The overload relay lockout control method according to claim 1, characterized in that, Step 1) The two preset operating modes are parallel operating mode and split operating mode: the blocking threshold in parallel operating mode is 85% of the rated current of the power equipment, and the blocking threshold in split operating mode is 100% of the rated current of the power equipment; the reset ratio in both operating modes is preset to 20%.

6. An overload relay interlocking control system, used to execute the method according to any one of claims 1-5, characterized in that, It includes a signal acquisition layer, a transmission layer, a main control layer, an execution layer, and a human-machine interaction layer that work in sequence. The specific working steps are as follows: Signal acquisition layer: The load current signal is acquired through the current acquisition submodule, and the switch position signal is acquired through the switch position acquisition submodule; Transmission layer: The switch position signal acquired by the switch position acquisition submodule is transmitted to the main control layer through the wireless transmission submodule or the fiber optic transmission submodule; Main control layer: Receives load current signal transmitted from signal acquisition layer and calculates effective current value; receives switch position signal transmitted from transmission layer and matches operating mode and interlocking parameters; executes interlocking logic judgment and reset judgment. Execution layer: Receives control commands from the main control layer and drives relays to output interlock or reset signals; Human-machine interaction layer: Displays the current switch position status, current effective value and lockout status, and provides operation interfaces for parameter setting and mode switching.

7. The overload relay interlocking control system according to claim 6, characterized in that, The working process of the signal acquisition layer in step 1) includes: The current acquisition submodule connects to the load current through a non-polar current input terminal. The current signal is converted into a digital signal by a high-precision AD chip and then transmitted to the main control layer. The high-precision AD chip is a ΔΣ type AD chip, which is used to ensure the accuracy of current acquisition. The switch position acquisition submodule receives the switch position no-contact signal through the switch position signal terminal, and transmits it to the transmission layer after being processed by the optocoupler isolation circuit. The optocoupler isolation circuit is used to achieve electrical isolation between the switch position signal and the internal circuit of the system.

8. The overload relay interlocking control system according to claim 6, characterized in that, Step 3) The main control layer's operation includes: calculating the effective value of the current by executing the root mean square value algorithm through the main control chip, pre-setting a database of interlocking parameters for two operating modes, and calling the corresponding parameters according to the switch position signal; the wireless transmission submodule of the transmission layer operates in the 2.4~2.5GHz ISM band, and the optical fiber transmission submodule supports parsing the location messages output by the power equipment intelligent terminal; the relay drive circuit of the execution layer converts the level signal output by the main control chip into a relay coil drive current through a transistor, driving the relay contacts to operate, and the drive circuit is equipped with a freewheeling diode to prevent the reverse electromotive force when the relay is disconnected from breaking down the transistor.

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