In this article we will not be covering safety aspects. Safety in connections is based upon corporate rules and regulatory requirements which can change while this article is available. Please ensure that you are working in a safe manner whenever dealing with electrical connections.
We will cover some concepts around how connections are made in low voltage variable frequency drive and medium/high voltage applications.
EPlug Connections
The EMPATH was the first system with a designed and mounted ePlug for the power industry. It maintains the most compact ePlug with commercially replaceable components other than the device. Unlike other devices it measures about 2.5 in x 2.5 in x .5 in high with direct PT or up to 700 Volts directly connected, and connected instrument grade CTs. The kit includes a small pass-through Cat 5e connector from the device to door. It is also used with the continuous monitoring system.
In the above picture, the device is on the right side, Cat 5e cable to the door connector, and voltage leads and CTs to the motor leads. For more information see the ePlug page. Red arrow to the ePlug connector in the image below.
Variable Frequency Drives
In the above VFD connected to a 400 horsepower pump motor at 460 Volts, the current clamps are placed around one of three conductors per phase and the voltage clip to the connection for each phase. The benefit of the construction of the EMPATH system is that it can be placed in the cabinet and the USB cable to the laptop can be run through an opening or vent. In the case of the above system, the drive was de-energized for the brief time it took to connect the EMPATH and connections were made without having to disengage any safety covers. In addition to data collection, the system was allowed to perform continuous monitoring for a period of time to identify transient defects in the pump system. A CT ratio of 3 is applied in this case and current unbalances may be evaluated in-depth if required.
Additional note: All three cables for each phase could be monitored with a BNC connected Rogowski coil. The EMPATH software allows the mV per Amp to be adjusted.
In this 400 Hz, 500 kW, 460 Volt application, connections were made and all of the leads were brought through a low voltage compartment. The area in front of the door is still clear during operation of the equipment during testing.
Medium Voltage Application
For medium voltage applications where an ePlug is not available (pre-installed), the EMPATH may be connected to the voltage and current connections on the relays or even the back of analog PT and CT outputs. This may take some work in determining where to connect the first time.
Once connected, the data is collected normally. With the EMPATH provided current clamps, select the high current selection of 150 or 200 Amps. Selection of the low current setting will filter out some of your data on the supplied CT. The higher setting allows for the extreme resolution of the EMPATH system which we can then use to see peaks on motors operating unloaded and uncoupled which no other technology can perform as cited by EASA in their study of other manufacturers’ tech. EMPATH does not require >50% load and can detect conditions as low as 0% load, even on a VFD. The voltage and current ratios are entered into the software before or after data collection.
Another option with the relay system is to add BN connections to the voltage connections on the system as shown below.
Alternate Connections
On occasion, there is no easy or safe way to connect voltage, as well. In these instances, at least one current clamp (or three) can be connected and the EMPATH will calculate findings based upon Current Signature Analysis only. In the case of needing torsional readings, kW, advanced power quality analysis or generators both voltage and current are necessary.