Saturday, March 27, 2010

DCU in R-APDRP - Issues and Concerns

Many states in R-APDRP have specified Data Concentrator Units for meter data acquisition from Sub-Station meters, which also is required to have Digital I/O's as well as Analog Inputs. The primary objective of the IT Portion of R-APDRP was to collect meter data for energy audit and develop the base line for losses. The DCU is an ideal solution for sub-station meter data acquisition alone. Once IO's are added and remote monitoring and control of substation equipment is also added as a must functionality of the DCU there are some important issues that arise.

The key aspect is the right product for this requirement. RTU's in Sub-stations are ideally suited for real-time monitoring and control requirements in sub-station including reading of MFT's which are essentially meter data. RTU's are designed for sub-station IO applications, are more rugged, support communication protocols like IEC 101/104 which are suitable for tele-metery applications in power systems.

However, once a Meter Data Concentrator is also expected to do an RTU function, with IO's, is as rugged as an RTU, should support real-time control, and also support real-time meter reading from Energy Meters, the requirements expected of the DCU changes. One of the most critical aspects in any device that is deployed in a sub-station is the EMI/EMC levels they support. Most Metering DCU's and Industrial Gateways are not suited for Sub-station requirements. Most of them have isolation at the communication and IO ports which are far lower than required in an sub-station environment. Most of metering DCU do not support the telemetry protocols required in a SCADA/DMS scenario. Expecting metering protocols like Modbus in R-APDRP to be used for remote control from an IT system of an automation asset like sub-stations would not be the right approach.

The right way to approach this would be to specify the right DCU requirements so that it can run-in a Sub-Station. In my opinion some of the key requirements would be the hardware specifications such that they can withstand the sub-station environment and the communication requirement such that the metering and control functions work seamlessly, for future applications as well.
  • EMI/EMC Specifications that are atleast comparable to IEC 60870-5-2 for RTU applications both for IO and communication ports. Atleast +/- 2 kV Surge protection and 8/15 kV Contact / Air Discharge and +/- 4 kV fast transient support are critical for the product to with stand sub-station conditions in the long run.
  • Protocol support for both metering and automation requirements - DLMS/COSEM, Modbus, IEC 60870-5-104. If remote control is required, then it should be through IEC 104 protocol and should support a future integration with SCADA System.
There has been incidence of many products failing in the field, because of lack of isolation of their serial ports damaging or burning the DCU or the Modem connected to the Meter. The right need for R-APDRP is a DCU that is a sub-station rugged meter data concentrator. So, it is always better to restrict to this specific requirement.

If IO's are required for any specific business process of an Utility, it would be better to provide for them using an external IO to the DCU, which can be controlled by a protocol, and if possible, provide for Sub-station hardened FRTU's with minimal expansion and IEC 101/IEC 104 protocols, so that in future when a SCADA system is implemented, the same IO's can be re-used, and in the interim, the DCU can be used for very rare / but critical controls.