SPI4000 smart primary injection test system

The SPI4000 sends output pulses that are 130 % of the maximum trip time on the curve. When testing with a generic breaker form, make sure the maximum trip time is correctly filled out. If necessary, the advanced setting will enable you to configure a longer pulse duration.  

To perform long-time pickup tests, the SPI finds 80 % of the pickup current, then gradually increases the current. You are then prompted to press the “Simulate Breaker Trip” button on the top right of the screen when pickup occurs, as indicated by the light on the breaker’s trip unit which will be blinking or remaining solid. Next, the SPI begins to decrease the current, and you should press the button again when the pickup drops out, indicated by the pickup light turning off on the trip unit. Finally, the SPI increases the current once more, this time at half the speed of the initial increment. You should press the button a third time as soon as the pickup indicator/light comes on again. This process enhances the accuracy of the recorded pickup current. If the long-time pickup is not recording accurately, the user can select “advanced settings” before the test to configure the ramp. The time can be slowed down if it’s occurring too quickly for you, enabling you to avoid inaccuracies. 

For proper operation, the unit must be connected to earth/ground (hereafter referred to as ground). The output will not be energised unless the unit detects a secure grounding connection. Please ensure that there is a solid and secure connection to ground. 

During an instantaneous pickup test, the SPI will first ramp up to 80 % of the requested current and then continue to ramp up to the requested current. If 80 % of the requested current trips the breaker, then the “Lower Starting Current” message will appear. This indicates that the starting current was too high and caused the breaker to trip before it could reach the requested current.  

There are several ways to address this issue. You can lower the requested current to ensure the starting current is below the breaker’s trip threshold. Alternatively, you can adjust the settings to reduce the percentage of requested current from 80 % to 60 % or 70 %. Additionally, it’s worth checking the short-time settings on the breaker’s trip unit, as unadjusted settings can also cause the breaker to trip prematurely before reaching the instantaneous pickup current.  

Two primary factors significantly influence the output current achievable from any primary injection test set.  

1. Input voltage – The output magnitude is proportional to the input voltage. If you have a weak source or high resistance input leads, these factors can result in a reduction in output power. 

2. Connections to the test specimen – Connections to the test specimen have a considerable effect on the current magnitude the instrument can deliver. Connection through the breaker stabs is crucial and can introduce resistance. Ensure a proper connection is established through the stabs and the proper bus size is being used. If the stabs are loose in the finger clusters of the breaker, it might be possible to add bus spacers between the test set stab and the breaker connection to further tighten the connection. If using flexible stabs, the output current will be reduced as this type of conductor has a higher resistance when compared to solid connections. For example, to push 30 000 amps through a breaker at 10 V, the output circuit resistance must be 330 micro-ohms or below. Any extra bus or a loose connection will add resistance and quickly limit the amount of current the unit can deliver. 

Proper primary injection testing of low voltage circuit breakers (LVCB) will confirm that they trip at the correct times and can properly isolate a fault. A coordination study is performed, and parameters are set to minimise the amount of interruption to other equipment. The characteristics of the circuit breakers are presented in the form of trip curves, and each circuit breaker will have a unique trip curve published by the manufacturer. The trip curves will have bands, or limits, that show how long it takes for the circuit breaker to trip when a certain amount of current is applied; the current is typically presented in multiples of the rated current. As long as the circuit breaker trips within the specified band, it operates correctly. You may perform up to four primary injection test types to verify that the LVCB is working correctly: a long time test, short time test, instantaneous test, and earth/ground fault test. The long, short, and ground fault tests all have a delay component. In contrast, the instantaneous test trips the circuit breaker immediately.

The long time test is a test of the overload function and requires two settings. The first setting is the pickup, which determines the load current level that is tolerable before an overload condition occurs. The second setting is the time delay that determines how long the overload condition is acceptable. Systems are generally designed to handle overload conditions for a short time. Still, damage will occur if the overload persists for too long. You typically perform a long time test at 3 times the rated current.

The short time test is also an overload test with a pickup time like the long time test but has a shorter duration with a higher current. Typical currents are at 6 times the rated current. A short time setting on the breaker is used to allow high current loads for a short duration, for example, a motor starting.

The instantaneous trip conditions test the breaker under fault conditions. Therefore, there is no intentional time delay built in, and the breaker should trip within milliseconds. If the circuit breaker fails to trip and clear the fault, this may result in damage to equipment or personnel. Additionally, an upstream breaker may need to clear the fault, resulting in other electrical system components unrelated to the fault being shut down. An instantaneous trip is typically tested using 8 to 12 times the rated current.

An earth/ground fault trip in the circuit breaker occurs when higher-than-normal currents flow through the ground path. Like the long time and short time functions, the ground fault has both a pickup current and a delay time. Both can be adjusted to fit the coordination study. There is typically a maximum delay that is permitted from ground fault conditions.

Each test is performed separately for each phase. As long as the trip time falls between bands on the time-current curves, the circuit breaker is considered to be in working condition.

Note: the ground fault sensor must be disabled to test long, short, and instantaneous trips.