IEEE C37.93-1987

IEEE C37.93-1987 is a technical guide for power system protective relay applications that use audio tones over telephone channels. It focuses on how tone-based signaling can support relay communication in utility and industrial power networks, where dependable coordination is important. The document is relevant to engineers working with protective relaying, channel selection, and system integration, helping define a consistent approach for designing and applying this type of communication scheme.

What is IEEE C37.93-1987?

This standard provides guidance on the application of audio tones for protective relay use over telephone channels. In that context, IEEE C37.93-1987 helps define a practical framework for transmitting control or protection-related information between relay endpoints using voice-grade communication paths. It is intended for power system applications where relay performance depends on reliable channel behavior, appropriate tone selection, and suitable interface practices. As a superseded document, it remains useful as a reference for legacy systems and historical engineering requirements.

Where is IEEE C37.93-1987 used?

IEEE C37.93-1987 is typically used in utility protection schemes and related power system installations where audio-tone signaling over telephone channels connects protective relays. It may be relevant to substation-to-substation communication, transmission line protection, and other relay coordination arrangements that depend on channel-based signaling. The guide is also useful in planning, reviewing, or maintaining legacy protective relay systems where telephone circuits and tone equipment are part of the communication path.

Why is IEEE C37.93-1987 important?

This guide matters because protective relay communication must be dependable and well understood. IEEE C37.93-1987 supports clearer design decisions for tone-based channels, helping reduce misapplication, improve coordination, and support more consistent engineering practice. For procurement and maintenance teams, it can also provide a useful reference when comparing equipment behavior, reviewing system compatibility, or working with older installed systems. In protective applications, that kind of clarity can help limit operational risk.

• Protective relay tone applications
• Telephone channel communication
• Power system coordination
• Legacy utility protection systems
• Channel and interface guidance