Author:
Dr. Ahmed El-Rasheed, Industry Director – Renewables, Megger
Date
09/01/2023
PDF
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Figure 1. Handheld instruments are convenient ways of checking EV charge points as part of your regular maintenance program.
The adoption of electric vehicles is a megatrend globally and especially in the USA. Massive federal, state, and private investments are driving an exponential increase in the network of chargers across the U.S. This is causing a significant impact on the existing electrical grid and a greater demand on electricity generation needs. Additionally, there are substantial maintenance needs that are also increasing. From an Inside E.V.s article:
“According to J.D. Power’s Electric Vehicle Experience Public Charging Study, quoted by Automotive News, the number of failed charging attempts grew from 15 percent in the first quarter of 2021 to more than 21 percent by the third quarter of 2022. At worst, almost 2 in 5 visits to chargers – or 39% – were unsuccessful last year.”
Several other reports provide similar statistics pointing to the need for periodic on-site testing. This on-site testing is needed even though most Electric Vehicle Supply Equipment (EVSE) comes with the latest technology that provides remote telemetry. In principle, the telemetry data should reveal hazards and charging problems without the need to physically go the EVSE. However, as the reports show, relying on remote telemetry alone results in unsuccessful charging of electric vehicles in almost 2 out of 5 visits.
Therefore, it is necessary to have on-site physical testing even after installation to periodically:
These on-site periodic checks help ensure a smooth, safe and efficient operation that brings a great Return-On-Investment (ROI).
On-site Testing
The testing of EVSE’s should include at least seven tests: four for safety, a check for nuisance tripping, and two operational tests. Therefore, performing the tests in a specific sequence with safety checks first is vital. The recommended tests are:
A good checking tool such as the EVCC300 from Megger, see figure 1, will run through each of these tests and provide a Pass/Fail result. The presence of any voltage on the frame or the ground conductors is a problem because it is a direct risk of electric shock to the user. This is a critical safety test and if it shows a voltage present then this problem must be fixed before any other work is done.
If a voltage is present on the frame, then a check of the protective Earth connection and its resistance value can determine the cause of this safety issue. The presence of a protective Earth connection can be verified with visual inspection, but a continuity resistance measurement is necessary to measure the resistance value. The lower the value the better the quality of the protective Earth connection.
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Figure 2. With the increased demand of electric vehicles, charging stations are being installed throughout the country
Most charge points will have a safety disconnection device installed, such as a GFCI (Ground Fault Circuit Interrupter). These devices must be inspected and tested for correct operation. A good GFCI will protect people and equipment from fault currents. They should also be tested to ensure that they don’t trip/disconnect at lower-than-expected settings because this can lead to false tripping (or nuisance tripping).
During the charging operation there is continued communication between the EVSE and the EV. However, if this communication is interrupted for any reason, then the charge point must stop supplying power. This is an important safety precaution that an inspection tool must test for and provide a Pass/Fail result.
The function of a charge point is controlled by the communications between the EV and the charge point. Therefore, the primary functionality test is a check of the communication protocols.
The charge point must have its Proximity Pilot (PP) signal tested. This is the communication signal that informs the charge point about the presence of an EV. The J1772 control pilot signal protocol is the standard communication method between the EV and the EVSE, see Table 1 for the breakdown.
Then there are several settings of the Control Pilot (CP) set current such as No Current, 13A, 20A, 30A, 50A, 80A and others. This determines the maximum current that will be supplied during charging. The CP is an essential piece of communication that allows for most efficient and safe charging. It is critical to provide the appropriate power to the connected EV, because too much power can damage the EV and too little will not charge it. Also, it is best to reduce the amount of current as the EV batteries are charged up, because the reduction of charge current as the batteries reach 100% capacity limits overload, heating, and damage.
The other important communication protocol of the Control Pilot (CP) signal is the charging status. The CP has various status states such as A (no vehicle connected), B (EV connected but not ready), C (EV ready to charge), D (EV ready to charge with ventilation required), and E (error).
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Subsequently, testing the Performance verifies that the charge point is supplying the power needed and with acceptable quality. This requires a discharge testing unit with power quality analysis.
Charge points could be high power like 350kW or a small residential unit supplying just 0.7kW, but in all cases a verification of the voltage and current output should be done. A discharge tester is commonly used to test batteries and discharge them onto a known load. However, these discharge testers can be used to test the EV charge point itself. Having a known load that behaves the same way each time allows for accurate determination of any degradation or other problems over time.
Also, analysis of the power quality (PQ) in terms of harmonics and distortions is part of good maintenance practice. PQ analysis is done by logging the output current and voltage over time. Good PQ analyzers will automatically detect and report distortions, phase shifts, and harmonics among other parameters. This power verification ensures that customers do get the power they pay for. And the quality analysis helps identify causes of errors and safety disconnections.
Conclusion
Using good testing practice with the right tools is critical to the safe and correct operation of charge points. It is highly recommended that charge points are fully tested at installation and after repair. Most charge points have sensors sending back information to a control center however a periodic check is still necessary to ensure that the sensor information is correct. Therefore, it is still recommended to have a periodic charge point check as part of the maintenance procedure.
There will be more than a million charge points installed over the next few years, and they will provide a good revenue stream for commercial owners and utilities. However, they must be installed and maintained in order to function correctly and safely.
