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Transformer core, and Troubleshooting
Transformer winding and the iron core is to pass, the main components of the electromagnetic energy conversion. * Ensure that they can run an issue of concern. Statistics show that the core problems caused due to failure, accounting for total transformer accident third. Manufacturing defects of the transformer core has attracted attention, and in the core can be * ground, the core ground surveillance, and to ensure that the ground have carried out technical improvements. Operational departments to detect and locate faults mentioned core considerable height. However, the transformer core fault still frequently occurs, the main reason is due to the multi-core and core grounding caused by poor grounding. Now two ways to judge and deal with cases of failure to make a presentation.
1 core normally need a little grounding reasons
Transformer during normal operation, the presence of an electric field between the charging winding and tank, while iron and other metal components in the electric field. Because of the uneven distribution of capacitance, field strength varies, if the core is not available * grounded, the charge-discharge phenomenon will produce, destroy the dielectric strength of solid insulation and oil, so the core must be * a little ground.
Core made of silicon steel sheets, in order to reduce eddy currents, there is a certain degree of insulation between the sheet resistance (typically only a few ohms to tens of ohms), due to the inter-chip capacitance is great, in an alternating electric field can be regarded as path, and thus the core In just a little ground to the whole stack of core laminations clamped at ground potential.
When the core or metal structures subject to two or more points (multi-point) is grounded, then the ground will cause between a closed loop, it is key chain portion flux induced electromotive force, and the formation of a loop, resulting in local overheat and even burn core.
Only a little grounding transformer core, is available * normal ground. That is the core must be grounded, and must be a little ground.
Core failure is mainly caused by two reasons, one is bad construction process caused by short circuit, the second is due to the attachment and multi-point grounding caused by external factors.
2 core multi-point grounding type
(1) After completion of the installation of transformers, not the tank top cover transportation positioning pin upside down or removed, the multi-point grounding.
(2) Since the core clamps limbs board stem from too close, tilt core laminations for some reason, the touch to clip leg plate, forming a multi-point grounding.
(3) iron yoke screw bushing is too long, and yoke laminations collide, constitutes a new ground.
(4) under the iron clamps mat insulation board between the foot and the yoke off or damaged so feet touching the yoke of the laminations causing ground.
(5) having a transformer and medium-sized submersible pump means, since submersible pump bearing wear, metal powder into the tank, sedimentation tank bottom, the electromagnetic force formed under the bridge, the lower yoke and feet or bottom is turned on, the formation of multi- Grounding.
(6) The oil-immersed transformer tank cover thermometer seat is too long, and the clip or yoke, next to the column edge collide, constitute a new ground.
(7) The oil-immersed transformer tank fell into the metallic foreign body, foreign body such metals and cabinet configurations enable core laminations pass, a ground.
(8) under the wooden yoke clamps and stepped between the pad surface damp or dirty, with more sludge to the insulation resistance value is reduced to zero, constitute a multi-point grounding.
More than three-point grounding when abnormal phenomenon
(1) generating eddy currents in the iron core, iron loss increases, local overheating of the core.
(2) multi-point grounding serious, and untreated for a long time, it will lead to continuous operation of transformer oil and winding too hot, so the gradual aging of oil-paper insulation. Will cause the core laminations two insulating layers aging and loss, overheating will cause greater core, the core will be burned.
(3) multi-point grounding for a long time, so immersed transformer oil degradation and produce a combustible gas, the gas relay.
(4) because the body of the core overheated pads and clamps carbonized wood.
(5) multi-point grounding causes severe blow grounding wire, the transformer loss of the normal point grounding, the consequences could be disastrous.
(6) multi-point grounding will cause a discharge phenomenon.
Ground fault detection over 4 points
Core multi-point grounding fault diagnosis method is usually detected in two ways:
(1) Gas chromatography analysis. As higher gas chromatographic analysis of methane and olefin component content, and carbon monoxide, and carbon dioxide gas content and little change compared to the past, or the content of normal, then the core overheating, the core overheating may be due to the multi-point grounding cause.
Chromatographic analysis When acetylene gas, indicating the core intermittent multi-point grounding has occurred.
(2) whether the measured ground current. It may be cited on the ground outside the casing in the transformer core grounding wire, with a wire clamp meter to measure whether there is current. When the transformer core properly grounded, because no current loop is formed. Grounding line current is very small, as milliamps (typically less than 0.3A). When there is multi-point grounding, the core main flux equivalent to a short circuit turn around the presence of flowing circulation inside turns, its value is determined and the relative position of the point of failure in the normal ground that shorted turn in the number of magnetic flux enclosed. Generally up to tens of amps. Have ground lead in using the measured current, very accurately determine the presence or absence of core multi-point grounding fault.
Exclude more than five-point ground fault
(1) Temporary exclusion method when the transformer can not outage:
① outer lead ground wire, if the fault current is large, you can temporarily turn the ground running. But the need to strengthen surveillance, after the disappearance of the iron core to prevent the fault appears floating potential.
② If the multi-point grounding fault belongs to unstable angina, grounding lines in a slide resistance in series so that the current is limited to 1A or less. Slip-line resistor selection is current grounding wire will work to open the measured voltage divided by the ground line.
③ use chromatographic analysis to monitor gas production rate point of failure.
④ by measuring find the exact point of failure, if can not handle, you can work properly grounded piece core is moved to the same location of the fault to a more substantial reduction in circulation.
(2) overhaul measure. After monitoring found that the existence of multi-point grounding transformer fault, the transformer can be shutdown, outage should be timely, complete elimination of multi-point grounding fault exit. The troubleshooting method, based on multi-point grounding type and reason, should take appropriate measures overhaul. But there are some cases, a power outage can not find the point of failure after hanging core, in order to find the exact ground, the scene may be as follows.
① DC law. The core and connecting piece clamps open, on both sides of the pass into the silicon steel yoke 6V DC, then DC voltmeter to measure the voltage silicon successively between levels, when the voltage is equal to zero or table indicates the reverse, the HERE is the fault can be considered ground.
② AC method. Low-voltage winding of the transformer is connected to AC voltage 220 ~ 380V, this time in the core there is flux exists. If there are multiple point ground fault occurs, the measurement will appear with a milliammeter current (core and connecting piece clip should be open). Along with a milliammeter yoke levels measured by point, when the milliammeter current is zero, then where is the fault.
1 core normally need a little grounding reasons
Transformer during normal operation, the presence of an electric field between the charging winding and tank, while iron and other metal components in the electric field. Because of the uneven distribution of capacitance, field strength varies, if the core is not available * grounded, the charge-discharge phenomenon will produce, destroy the dielectric strength of solid insulation and oil, so the core must be * a little ground.
Core made of silicon steel sheets, in order to reduce eddy currents, there is a certain degree of insulation between the sheet resistance (typically only a few ohms to tens of ohms), due to the inter-chip capacitance is great, in an alternating electric field can be regarded as path, and thus the core In just a little ground to the whole stack of core laminations clamped at ground potential.
When the core or metal structures subject to two or more points (multi-point) is grounded, then the ground will cause between a closed loop, it is key chain portion flux induced electromotive force, and the formation of a loop, resulting in local overheat and even burn core.
Only a little grounding transformer core, is available * normal ground. That is the core must be grounded, and must be a little ground.
Core failure is mainly caused by two reasons, one is bad construction process caused by short circuit, the second is due to the attachment and multi-point grounding caused by external factors.
2 core multi-point grounding type
(1) After completion of the installation of transformers, not the tank top cover transportation positioning pin upside down or removed, the multi-point grounding.
(2) Since the core clamps limbs board stem from too close, tilt core laminations for some reason, the touch to clip leg plate, forming a multi-point grounding.
(3) iron yoke screw bushing is too long, and yoke laminations collide, constitutes a new ground.
(4) under the iron clamps mat insulation board between the foot and the yoke off or damaged so feet touching the yoke of the laminations causing ground.
(5) having a transformer and medium-sized submersible pump means, since submersible pump bearing wear, metal powder into the tank, sedimentation tank bottom, the electromagnetic force formed under the bridge, the lower yoke and feet or bottom is turned on, the formation of multi- Grounding.
(6) The oil-immersed transformer tank cover thermometer seat is too long, and the clip or yoke, next to the column edge collide, constitute a new ground.
(7) The oil-immersed transformer tank fell into the metallic foreign body, foreign body such metals and cabinet configurations enable core laminations pass, a ground.
(8) under the wooden yoke clamps and stepped between the pad surface damp or dirty, with more sludge to the insulation resistance value is reduced to zero, constitute a multi-point grounding.
More than three-point grounding when abnormal phenomenon
(1) generating eddy currents in the iron core, iron loss increases, local overheating of the core.
(2) multi-point grounding serious, and untreated for a long time, it will lead to continuous operation of transformer oil and winding too hot, so the gradual aging of oil-paper insulation. Will cause the core laminations two insulating layers aging and loss, overheating will cause greater core, the core will be burned.
(3) multi-point grounding for a long time, so immersed transformer oil degradation and produce a combustible gas, the gas relay.
(4) because the body of the core overheated pads and clamps carbonized wood.
(5) multi-point grounding causes severe blow grounding wire, the transformer loss of the normal point grounding, the consequences could be disastrous.
(6) multi-point grounding will cause a discharge phenomenon.
Ground fault detection over 4 points
Core multi-point grounding fault diagnosis method is usually detected in two ways:
(1) Gas chromatography analysis. As higher gas chromatographic analysis of methane and olefin component content, and carbon monoxide, and carbon dioxide gas content and little change compared to the past, or the content of normal, then the core overheating, the core overheating may be due to the multi-point grounding cause.
Chromatographic analysis When acetylene gas, indicating the core intermittent multi-point grounding has occurred.
(2) whether the measured ground current. It may be cited on the ground outside the casing in the transformer core grounding wire, with a wire clamp meter to measure whether there is current. When the transformer core properly grounded, because no current loop is formed. Grounding line current is very small, as milliamps (typically less than 0.3A). When there is multi-point grounding, the core main flux equivalent to a short circuit turn around the presence of flowing circulation inside turns, its value is determined and the relative position of the point of failure in the normal ground that shorted turn in the number of magnetic flux enclosed. Generally up to tens of amps. Have ground lead in using the measured current, very accurately determine the presence or absence of core multi-point grounding fault.
Exclude more than five-point ground fault
(1) Temporary exclusion method when the transformer can not outage:
① outer lead ground wire, if the fault current is large, you can temporarily turn the ground running. But the need to strengthen surveillance, after the disappearance of the iron core to prevent the fault appears floating potential.
② If the multi-point grounding fault belongs to unstable angina, grounding lines in a slide resistance in series so that the current is limited to 1A or less. Slip-line resistor selection is current grounding wire will work to open the measured voltage divided by the ground line.
③ use chromatographic analysis to monitor gas production rate point of failure.
④ by measuring find the exact point of failure, if can not handle, you can work properly grounded piece core is moved to the same location of the fault to a more substantial reduction in circulation.
(2) overhaul measure. After monitoring found that the existence of multi-point grounding transformer fault, the transformer can be shutdown, outage should be timely, complete elimination of multi-point grounding fault exit. The troubleshooting method, based on multi-point grounding type and reason, should take appropriate measures overhaul. But there are some cases, a power outage can not find the point of failure after hanging core, in order to find the exact ground, the scene may be as follows.
① DC law. The core and connecting piece clamps open, on both sides of the pass into the silicon steel yoke 6V DC, then DC voltmeter to measure the voltage silicon successively between levels, when the voltage is equal to zero or table indicates the reverse, the HERE is the fault can be considered ground.
② AC method. Low-voltage winding of the transformer is connected to AC voltage 220 ~ 380V, this time in the core there is flux exists. If there are multiple point ground fault occurs, the measurement will appear with a milliammeter current (core and connecting piece clip should be open). Along with a milliammeter yoke levels measured by point, when the milliammeter current is zero, then where is the fault.