Source: Alliance of Electrical Experts
Our substation battery is similar to a mobile phone battery, and proper charging and discharging can extend the life of the battery.
In the past, the method of boiling water and boiling water in an electric furnace was used to discharge the nuclear capacitance. And now we use a discharge meter to discharge.
What should I pay attention to when using a discharge meter?
The battery (group) is in a floating state for a long time, and after a long time, the electrode will be covered by a thick oxide film, which causes the anode plate of the battery to be passivated, the internal resistance of the battery gradually increases, and the actual capacity of the battery is much lower than its nominal capacity.
VRLA batteries, commonly known as "maintenance-free batteries", are widely used in power systems, and "maintenance-free" only means that there is no need to add water, acid, and liquid, and daily testing and maintenance work is still indispensable. Because the performance of the battery will deteriorate due to the undercharge, overcharge, overdischarge, and high ambient temperature of the battery in operation, only the verification discharge can objectively and accurately measure the true capacity of the battery, and ensure the reliability of the operation of the DC power system.
What is the concept of battery capacity?
Battery capacity is the amount of electricity that the battery can give under certain discharge conditions;
The capacity of the battery (ampere-hours) is equal to the product of its discharge current (amps) and discharge time (hours);
The rated capacity refers to the discharge capacity calculated when the discharge time is 10 hours and the discharge end voltage is 1.8 volts;
For a nominal 2 volt 300 Ah battery, the discharge current is generally set to 10% of the capacity, i.e. 30 amps. If the discharge is terminated after 8 hours, it has an actual capacity of 30 x 8 = 240 (ampere), which is 80% of the rated capacity.
When the dual charging and dual battery system is discharged, what problems should be paid attention to when the DC system is closed?
When the double charge and double electric system is discharged, the loop closing operation of the DC system is a special mode of operation, because the two sets of DC systems each have an insulation monitoring device, so that the DC system has two virtual grounding points, which directly affects the judgment of the insulation monitoring device on DC grounding and the DC line selection function, therefore, it is recommended to release and close the grounding point of one of the DC insulation monitoring devices, and retain one of the sets of insulation monitoring devices for its alarm function.
In addition, after the discharge is completed, it is not suitable to immediately restore the loop closing mode to the open-loop operation (normal) mode, but to use a set of chargers to charge the discharged battery evenly, and the direct battery can be fully charged before it can be put into system operation and restore the normal open-loop operation mode.
It should be ensured that the rated voltage of the battery pack is consistent with the voltage level of the discharge meter. The rated voltage of the DC system of the substation (including the battery pack) is usually 48V, 110V, 220V, at present, there are many models of discharge meters sold on the market, there are a single voltage level (only applicable to 220V or 110V), there are adaptive (can be applied to three different voltage levels), there are a series of charging and discharging all-in-one machine. However, the most important one is to choose the rated voltage of the battery pack to be consistent with the use range of the discharge meter, otherwise, the discharge capacitance cannot be completed, and the discharge meter and the battery may even be damaged.
Screen 1: The first step in the operation is to check the battery and its connecting strips:
Picture 2: We can clean the battery while inspecting and recording the condition of the battery;
The key points of the visual inspection are:
Check that the battery is not damaged in appearance, swollen or broken pole;
The nameplate and number of the single battery are clear;
外壳清洁及无开裂变形、极柱无变形、损坏、锈蚀;
The exhaust valve has complete parts, no damage, no acid mist escape;
After the visual inspection, the whole group of batteries should be cleaned with a brush or rag.
Please look at the pictures
Picture 3: The battery has crystals;
Picture 4: Leakage from the upper cover of the battery;
Screen 5: terminal thiric acid;
Picture 6: Short circuit caused by leakage at the bottom of the battery;
Picture 7: After the visual inspection, the whole group of batteries should be cleaned with a brush or rag.
Next, let's check the problem with the connector:
Carefully check whether the connection of all connecting strips is tightened, whether there is corrosion in the connecting strips, and whether the voltage drop of the connecting strips exceeds 8mV.
The battery screw pole is fragile and not suitable for brute force fastening. It is more appropriate to do this: after one person tightens, the other person repeats the inspection;
According to the work instructions of the network company: in the battery pack, the internal resistance of a single battery is a substandard battery with a sudden change of 50% compared with the historical record.
This can be verified by further capacitance discharge. "Freezing three feet is not a day's cold", and the sudden increase in internal resistance is a sign of battery deterioration.
The corresponding battery capacity and internal resistance can be referred to the following table:
Capacity: 200 Ah Reference internal resistance is 0.70 mOhm;
The reference internal resistance of 300 Ah is 0.65 mOhm;
The capacity is 500 Ah and the reference internal resistance is 0.40 mOhm.
The larger the capacity, the smaller the internal resistance!
It is understood that in some places, the internal resistance test is directly used instead of the nuclear capacity test. What's wrong with that?
The internal resistance of the battery has been recognized as the decisive parameter for judging the capacity of the battery, and it is widely used because of the simplicity of the method. However, the accuracy of the internal resistance meter depends on the bite force of the clamp, and the data measured due to the difference in process or improper use method in the field are quite different. The verification capacity discharge can measure the capacity of the battery 100%, which is the most reliable method to detect the performance of the battery at present, and because the check discharge itself can play a certain role in the maintenance of the battery, the check discharge is not yet able to be replaced by other methods.
The fourth step in the process is the discharge operation:
Before discharging, we must connect the discharge meter and the battery pack.
The discharge meter and the battery pack are connected (note that the polarity is correct). The discharge meter + end (red) is connected to the positive terminal of the battery, and the discharge meter - terminal (black) is connected to the negative terminal of the battery.
When connecting, it is recommended to connect the discharge meter first,
The battery pack end is then connected, and this sequence of operations reduces the possibility of accidents caused by short circuits in the battery pack.
The discharge meter end is an empty terminal, and the battery pack is a live body, and it is easy to short circuit if the battery is connected first and the wire is held!
After the discharge meter is powered on, we can set the discharge parameters below.
Enter the discharge settings menu;
Set the voltage type of the battery pack (generally 220V or 110V, communication 48V)
Set the discharge current to 10% of the capacity, 500 A for 500 Ah, 30 A for 300 Ah (and so on)
Set the total termination voltage, 108 batteries, 1.8V termination, can be set to 108X1.8=195V;
set the end time and discharge capacity;
After confirming that the parameters are correct, the discharge will officially begin.
After the parameters are set, let's talk about the start and stop of the discharge meter.
The discharge meter is turned on for discharge!
After the parameter setting is completed, close the air switch on the wiring panel and officially turn on the discharge. The discharge meter is working properly and will display the discharge current and discharge time.
Automatic shutdown. The discharge detector has the function of automatic shutdown of undervoltage, so in the discharge process, especially in the later stage, the time and capacity may not be reached and the discharge detector will automatically shut down, which is a normal phenomenon, indicating that some batteries in the battery pack are in a state of power loss;
Discharge current fluctuations. During the discharge process, in order to ensure that the discharge current is constant in the state of continuous decline of the battery pack voltage, the discharge current of the discharge detector is constantly in dynamic adjustment, so it is normal for the discharge current to fluctuate slightly. However, for the sake of safety, the DC clamp meter is used to monitor whether the charging and discharging currents meet the requirements.
Below we will talk about the temperature and voltage measurement of the battery.
terminate the discharge;
After the battery is discharged to the termination voltage, it continues to discharge is called overdischarge. Over-discharge will seriously damage the battery, which is extremely unfavorable to the electrical performance and cycle life of the battery;
Batteries with different voltages have different termination discharge voltages. 2 volt battery with 1.80 volt termination, 6 volt battery with 5.40 volt, 12 volt battery with 10.80 volt termination;
End the discharge. When a certain discharge termination condition (time, capacity, voltage) is reached, the discharge detector will automatically stop discharging, and the user can also manually stop discharging in the process;
Separate the discharge detector from the battery pack. First disconnect the air switch on the wiring panel, and then the small switch on the control panel. After confirming that the discharge detector is completely powered off, remove the battery connection in the order of the battery pack first and then the discharge detector;
Picture 1: Fault 1, discharge stopped unexpectedly;
Picture 2: The discharge has just started, and the discharge meter has stopped discharging;
Picture 3: The solution is that some of the discharge meters need to be connected to the wiring to detect the total voltage, and the discharge meter will automatically stop discharging if the line is not connected!
The following is the troubleshooting of the battery that has lost power.
Picture 1: During the discharge process, there is a battery that obviously loses power and has insufficient capacity, how do we deal with it?
(Assuming it is #2 of the group) The capacity of the battery is insufficient, how do we isolate it and continue the nuclear capacity test.
Step 1: Stop discharging first, then remove (#2蓄电池) the connection with the adjacent battery, and exit the #2 battery;
Part 2: Connecting the Adjacent #1 and #3 Batteries;
It should be noted that if there is one less battery, the total termination voltage will be modified, and the detection unit of the battery pack will also be affected.
After the discharge is finished, let's talk about the static position of the battery.
After the discharge is terminated, the battery should be left to stand for at least 1 hour, the purpose of which is to completely stop the chemical reaction inside the battery and the temperature of the battery can also be lowered during this time. to continue charging it.
Why can't the discharged battery be put into operation immediately? Because the discharged battery needs to be restoratively charged, the charger should enter the uniform charge mode, and the DC system in the average charge mode will increase the voltage of the whole system (including the control bus) by 10V, and the duration is longer, such a high voltage will cause damage to the device, which is also not allowed by the regulations. Therefore, the correct way is to use the battery after the charger is charged and discharged, and then put into the system operation after being fully charged.
Fill in the test record;
Before and after discharge, the internal resistance and voltage of the battery should be measured once;
Record the internal resistance of the battery and its voltage data before and after discharge;
Measure the voltage of the battery unit every hour, measure the battery temperature and the ambient temperature;
Record the measured battery data every 1 hour;
And in the process, the data of the discharge meter is constantly monitored.