On-line Infrared Monitoring System for Substation Main Transformer

1. Overview

The main transformer is the main step-down transformer used for transmission and transformation in the substation, and is also the core part of the substation. The capacity of the main transformer is generally large, and the reliability of the work is high. Although the failure rate of the main transformer is not high, it will cause great loss once it breaks down. If not, it may cause equipment failure. Or it could cause a fire and endanger normal transportation. Therefore, it is of great significance to analyze the transformer fault reasons and take corresponding preventive measures.

The main transformer has the following faults:

Blockage of radiator caused oil temperature rise of main transformer

There are two main reasons for the high oil temperature: one part of the radiator has a small finned gap design and serious blockage between the radiator fins. Due to the low strength of the cooling air duct filter net installed on the locomotive's upper cover, it is stuck between the radiator fins after rupture, affecting the radiator ventilation; The upper fins of another part of the radiator collapsed in a large area, blocking the gap between the fins, so that the radiator ventilation reduced, affecting the heat dissipation effect.

A fault caused by a decrease in the insulating effect of solid materials

The aging of solid insulation material reduces the original insulation performance of the transformer, which is easy to produce partial discharge and cause breakdown damage of the transformer. There are three main reasons:

l The insulation effect of solid material is decreased because of heat

The transformer is overloaded for a long time, so that the temperature exceeds the allowable range of insulation material, resulting in the fracture of solid insulation polymer chain, resulting in the material becoming brittle and aging, thus reducing the insulation performance. Insulating oil overheating of H₂and solid insulation material at high temperature of CO, CO₂and C2H4, H₂gas lead to overheating insulation aging.

l The insulation effect of solid material is decreased due to electrical reasons

In normal operation, sudden three-phase short circuit occurs at the outlet of the main transformer, and the insulation of the transformer is displaced due to the electric power generated by the large current, resulting in the deformation of the coil. The three-phase short circuit at the exit caused by natural reasons and human factors will cause great harm, which will not only bring fatal damage to the main transformer, but also may lead to large area power failure. Partial discharge can cause branch discharge on the insulating surface. When the insulating material is subjected to high voltage electric field, discharges will occur repeatedly on its surface or in its internal space. The ion arc and ion movement generated will seriously erode the insulating material and reduce its insulating performance.

l The insulation effect of solid material is decreased due to environmental factors

If there is dust, moisture, corrosive gas, radiation and oil around the main transformer, it will accelerate the aging of solid insulation material and affect the insulation effect. Impurity ions are easy to cause ion current and ion collision, so the insulation material should also play a role of resistance to surrounding dust, gas erosion, but also to protect the associated conductor.

2. Demand Analysis

2.1 Industry Application Requirements

According to the common fault analysis of the main transformer in the integrated substation, the main transformer is accompanied by the rise of its own temperature before the failure of the main transformer. Therefore, in order to take effective protective measures, it is an effective means to judge the temperature of the main transformer. When the temperature reaches a certain high temperature value, the main transformer substation is judged to be abnormal, and corresponding measures should be taken to eliminate safety hazards.

2.2. Current Solutions

In order to accurately grasp the working conditions of the main transformer substation and find out the problems in time to avoid the property and safety losses caused by the abnormal work of the main transformer substation, various power stations take various measures, among which the temperature of the main transformer is measured by the temperature sensor to judge the working status of the main transformer.

The current temperature of the main transformer can be measured and its working state can be determined by the sensor temperature measurement. However, as the sensor temperature measurement is the temperature of a single point of the transformer, even if the multi-point placement sensor temperature measurement can only obtain local temperature information, so the measured temperature is not comprehensive and accurate enough. At present, the temperature measurement of the primary variable pressure device in a substation is under the pressure gun. When the temperature of the primary variable is too high, the fire control water gun will automatically trigger the water jet to cool down the primary variable inlet line. When the temperature sensor is inaccurate or abnormal, the loss caused by the fire water monitor is very serious. Therefore, a set of more effective methods are needed to measure the temperature of the main variable.

Shortcomings of current detection methods:

ü Local temperature measurement can not be used to determine the working state of the main temperature field.

ü The loss of water cannon treatment caused by temperature misjudgment is large.

3. Infrared Thermal Imager Scheme

Thermal imager uses infrared detector and optical imaging objective lens to receive the infrared radiation energy distribution pattern of the target to reflect on the photosensitive element of the infrared detector, so as to obtain the infrared thermal images. Different colors on the thermal images represent different temperatures of the object to be measured. The non-contact temperature measurement method of infrared thermal imager can measure the real-time temperature without affecting the operation of the main transformer, and take cooling measures when abnormal conditions are found.

When designing the on-line thermal imaging temperature measuring system of power station, we adopt the system solution of front-end infrared thermal imager + back-end processing software.

Front-end infrared thermal imager + back-end processing software system solution. The design method of separating front-end acquisition and back-end display also enables the staff to stay away from the scene of the dangerous work area, and the operation status of the equipment can be known in the control room, which is safe and efficient.

3.1 Dual-light Monitoring Method

The main transformer substation adopts infrared light + visible light dual spectrum monitoring mode to monitor the temperature field of the main transformer through infrared light. In case of abnormal temperature, an alarm signal is given to remind the staff to take effective measures. Visible light monitoring is assisted to monitor the situation within the field of view in real time, so that the staff can see the surrounding situation of the main transformer substation more clearly and make a correct judgment.

3.2. Add Temperature Measurement Object

Infrared thermal imaging temperature measurement is to measure the entire field of view within the scope of the temperature of each point, so may occur in the process of long-term temperature other than we focus on high temperature appeared in the field of view cause misjudgment, so we set the temperature object, the selection of the main transformer box through a polygon temperature measuring object for measuring temperature object, focus on the part of the temperature information, to prevent false positives.

3.3 Linkage of Alarm Signals

4. Review

Considering the user's actual usage, and the system reliability and economical consideration of the project, we will keep the original in the substation main transformer monitoring ways of monitoring to detect the infrared thermal imaging detection of signal and the original way of monitoring signal processing in series in the same management system, and that when there is alarm all monitoring way to trigger the fire water monitor for processing.

This way can effectively avoid the unnecessary call of fire and water monitor caused by the misjudgment of a certain monitoring method, which costs human and material resources. At the same time, the original system will be used to save resources.