Ethernet Hubs in Substations – What Standards Should Apply?

 from the Distributech Power Breakfast
March 2/3, 2000

This was the topic at DistribuTech Power Breakfasts chaired by your editor on March 2 & 3, 2000. PennWell was gracious in adding this breakfast topic at our request. The request had stemmed from discussions at the last Utility Initiative in San Diego on January 13 & 14.

At that time, the utilities were complaining that the hub vendors didn’t know what utilities needed in substation equipment. The hub vendors complained that each utility seemed to have its own idea of the appropriate standard. Thus the Power Breakfasts were organized. Each morning, there were utilities, hub vendors, relay IED vendors, and system integrators attending. 

For talking purposes, a draft document was prepared based in part on prior work done by Mark Simon – Commonwealth Edison Company, Chicago. It was also based on work underway in the PES Power System Relaying Committee to update IEEE Standard C37.90.1 – the SWC and Fast Transient standard.

The discussions were spirited, with some hub vendors questioning the need for extreme low temperature since the hubs will likely be in a control house with some heating. An engineer from Ontario Hydro pointed out that his utility had to start up substations that had been dead for three weeks in the winter, hence the requirement. There was no agreement that a single temperature range was appropriate, so the consensus was to define two ranges – one based on the existing IEEE Standard C37.90 (- 20 to + 55º C) and the other to cover more extreme requirements ( -40 to +85º C).

Due to its prevalence in the process control industry, an optional power supply rating of 24 V dc was added. A cautionary note was also added reminding vendors that the input dc side of all power supplies must be ungrounded.

Here is the draft document as it now stands. We encourage your comments.

Proposed Specifications for Substation Hardened Ethernet Devices (mostly based on existing standards)

(results of DistribuTech Power Breakfasts March 2 & 3, 2000 chaired by John Tengdin)

Temperature  (one of two ranges to be specified)

            Normal operating range of -20° C to +55° C (per IEEE Standard C37.90)

 or

Extreme operating range of  -40° C to +85° C

Surge Withstand and Fast Transient Voltages – Levels as defined in IEEE Standard C37.90.1

Transverse and common mode test voltages directly applied to the power supply terminals

Transverse and common mode test voltages directly applied to alarm terminals, if any

Common mode test voltages applied to metallic comm circuits via a capacitive clamp

Radiated Frequency Immunity  - as defined in IEEE Standard C37.90.2  

ll six sides of the device to be tested at 35 volts/meter radiated power

Power Supply Nominal Voltage Ratings: 24 Vdc, 48 Vdc, 110/125 Vdc, and 220/250 Vdc

Power Supply Over and Under Voltage  (range established in IEEE Standard C37.90 for dc auxiliary relays: minimum = 80% of rating, maximum per table) No internal ground

The equipment under test will be shut down and repowered after it reaches each temperature extreme. After the equipment’s input supply voltage is lowered to the point at which the equipment fails to operate, the voltage will be increased. The equipment’s ability to resume operation will be assessed.

Power Supply Input – One minute 50 or 60 Hz high potential test at a voltage of 1 kV to ground

Copper Ethernet Ports– One minute 50 or 60 Hz high potential test at a voltage of 1 kV to ground

Acceptance Criteria: Per attached pages 2 & 3

Prepared by John T. Tengdin, OPUS Publishing                                      Hub_Specs_06Apr00

Based on prior work by Mark S. Simon – Commonwealth Edison Company

Excerpts from draft 5 of proposed revisions to IEEE C37.90.1 “Surge Withstand Capability Tests for Relays and Relay Systems Associated With Electric Power Apparatus”

8.    Criteria for acceptance

8.1    Application of criteria

The criteria below shall apply to the equipment being directly tested, and any devices linked to the equipment via direct or remote connections.  Examples of the connections are current loops and voltage circuits (DC, audio, carrier, or microwave).  Serial, parallel, optical (fiber or infrared), and radio frequency connections apply as well.

 8.2    Conditions to be met

The equipment shall be considered to have passed the SWC tests if ‑ during, or as a result of, the tests ‑ all of the conditions below are met for the equipment and the connected devices:

1. The specified performance of the equipment, including the operating time, does not change, beyond stated tolerances.

2.  No hardware damage occurs.

3. No change in calibration beyond normal tolerances results.

4. No loss or corruption of stored memory or data, including active or stored settings, occurs.

5. "System resets" do not occur, and manual resetting is not required.

6. Established communications is not permanently lost (i.e., loss of channel or modem disconnections if reliability is in jeopardy).

7. Established communications recovers within an acceptable time period, if disrupted.

8. Communications errors, if they occur, do not jeopardize the protective functions.

9. No loss of digital pulse synchronization occurs, if the loss of synchronization affects externally observable device behavior which results in an out of tolerance condition.

10. No changes in the states of the electrical, mechanical, or communication signal outputs occur.  This includes alarms, status outputs, or targets.

11. No erroneous, permanent change of state of the visual, audio, or message outputs results.  Momentary changes of these outputs during the tests are permitted.

12. No error outside normal tolerances of the data communication signals (SCADA analogs) occurs.

Examples of protective communication configurations:

The following represents some example configurations and the tests required to comply with this standard.  Since equipment varies among manufacturers and application, these examples may not be entirely applicable but will act as a starting point in determining the required test points for similar designs.

Points that shall be tested and are common to all examples include:

1. Keying and output connection between the relay system and the telecommunication interface equipment.

2. Alarm and auxiliary I/O connections.

3. Permanently connected substation computers.

4. The power supply inputs to each device.

5. In the situations involving multiplexers that are transporting non-protection logic signals,  the non protection inputs are to be tested with observations made on the Protection Logic signals. 

6. Connections between telecommunication interface and telecommunications system equipment shall be tested unless these connections must, as stated by the manufacturer(s), be less than 2 meters in length.

Items that can be excluded from testing include:

1. Temporary connected maintenance computers.

2. Connections that, as stated by the manufacturer, must be less than 2 meters in length.

3. Non-metallic connections, such as fiber.

Figure D.1 Protective relay using Ethernet for protection logic and tripping output signaling