Encyclopedia

About Self Healing Ring Converters(Redundant Ring)

It’s important to note– that all self-healing ring methodologies are not alike. In fact, the term “self-healing ring” is frequently interpreted differently by end users and vendors alike. Vendor offerings vary greatly in terms of function, features and sophistication.

Before buying a system, end users should identify what they need in terms of a “self-healing” function and request specific details pertinent to these identified needs from the prospective vendor. For example, many vendor offerings can detect cable breakage only at the receiving side. Unless the device can detect failures at the transmit side, there is no way to know if the next device is receiving the signal.

Astute buyers also need to find out exactly what a vendor means when it advertises self healing functions. The term “self healing” often means something different to a marketing copy writer than it does to an engineering supervisor responsible for a give network. For example, many vendors offer a self-healing ring scheme that doesn’t separate broadcast and receive channels. As a result, activating the self-healing function can cause these channels to interfere with each other.

Bueno Electric offers self-healing ring functions in many of its Ethernet switches and fiber optic modems and multiplexers.

  • Ethernet Switches

    Most vendors offer IEEE Spanning Tree and Rapid Spanning Tree Protocol (STP, RSTP) to provide network redundancy. IEEE Spanning Tree Protocol (STP) discovers and fixes network loops to prevent broadcast storms. Spanning Tree (STP) will also automatically activate the redundant link if the primary link fails. It should be noted that mesh networks can only be configured using RSTP.

    Depending on the size and configuration of the network, the redundant feature of most Ethernet switches provide for automatic switchover to the secondary data path in less than 30-50 msec.

     

  • Fiber Optic Modems

    Several models of Fiber optic modems support self-healing ring topologies; however, the HFB series indsutrial ethernet switch is considered by many industry experts to be among the best available.

Many features are critical to network operation; some are unique for a product of this type. HFB series Self Healing Ring differs from competitor offerings in its sophistication. This sophistication enables it to build in a variety of user benefits often not available with many other vendor’s Self-Healing Rings.

These benefits include:

  • The HFB Slave unit provides loop monitor signal LEDs that detect if any incorrect fiber cables are connected.

    Solidly lit green LPA (Loop “A”) and LPB (Loop “B”) LEDs indicate a normal system; blinking green LEDs
    indicate that the wrong fiber cable has been connected. Some vendors do not offer any simple means to verify that the correct fiber optic cables are connected at remote nodes.
    This is absolutely critical! For example, if a technician inadvertently cross connects the Ring A and Ring B
    cables to a modem, the network will appear to function normally, but the Self-Healing portion will not be operable.
    Technicians must have specific diagnostics to pinpoint where the errant cable cross-connect has
    occurred.

  • The HFB series self-healing ring can detect faults both upstream and downstream from each unit.

    It can detect cable breakage at both transmit and receiving sides. Some vendor’s SHR products detect cable breakage only at the receiving side. Unless the device can detect failures at the transmit side, there is no way to know if the next device is receiving the signal (see adjacent diagram).

     

  • The HFB prevents any type of Echo effect

    Some vendors offer a self-healing scheme that doesn’t separate broadcast and receive channels. This often results in an “Echo” effect that can disable network communications. (”Echo” happens when the data signal transmitted into the Master unit, and around the ring, is received back at the Master unit’s port).

     

  • Each HFB (Slave) includes a Dry Contact Alarm which enables pinpointing any fault.

    Technicians must be able to pinpoint exactly where a fault has occurred. A dry alarm contact on the modem’s master unit indicates when self healing has occurred somewhere on the ring. Dry alarm contacts from the modem slave units on either side of a fault effectively pinpoint the location of the break or failure.

  • The HFB offers a Multiple-Master Self-Healing Ring Topology.

    This innovative configuration virtually doubles the reliability of a single Master because it can recover
    faults or failures in both rings A and B in two different places. System integrity is maintained because both Master units poll the Slaves at the same time, but through different “half” rings.

     

Fiber Optic Multiplexers

For legacy TDM network users, advanced fiber optic modems and multiplexers have made self-healing ring networks even more reliable. One such product that is particularly ideal for Protective Relay Networks in the Power Utility Industry is the Self Healing, Double Virtual Ring Multiplexer

Channel Mapping

Bueno Electric is specialized 12-Channel Self-Healing Ring Multiplexer features the potential benefits of Channel Mapping: increased reliability, cost savings through flexible channel configurations and faster polling rates.

Channel Mapping enables users to configure specific channels from the Master to designated Slave units on a fiber ring. Designated channels could include both a dedicated virtual point-to-point channel and a broadcast poll-response channel on each Slave.

The fiber ring is formed with two Master units, A and B, and several Slaves. Each Slave is daisy-chained through only two cores of fiber cable to form a multi-drop network. The slaves are connected individually to an IED type of Protective Relay to provide the communication functionality required by the IED Relay and/or the system.

In this case, Ch. 1A on all Slaves is connected to the poll-and-response serial port, either RS-232 or RS-485, of the IED Relay, and the SCADA Host computer. This channel is used to communicate the status, parameter download and control of the Relays.

Communication between the consecutive Relays is done via two separate and independent channels assigned to each relay. For example, Relay #2 is assigned with Ch. 3A & 3B for Relay communications; whereas, Relay #3 is assigned with Ch. 4A & 4B, etc.

For upstream communications, Relay #2 to Relay #1, Ch. 3A should be connected with Ch. 2A of Relay #1. This is achieved through the cross-connect at the Master A. For downstream communications, Relay #2 to Relay #3, and Ch. 3B should be connected with Ch. 4B of Relay #4. This is achieved through the cross-connect at the Master B.

The serial data streams sent and received between Relays will travel in the fiber at a speed of 6 micro seconds per kilometer and will terminate on the corresponding serial port of the two Masters, through the cross-connect, and on to the other serial port which is assigned to the upstream or downstream Relays.

It will then be broadcast by the two Masters in each direction over the fiber. This process enables the fiber monitoring function of the Masters to protect the communications channels. In the event of a break in the fiber, the Communications channels will be recovered by the Self Healing operation of the network.

The HFB Multiplexer can provide both regular Poll-and-Response type Multi-Drop communication capability as defined by DNP3.0 and Peer-to-Peer functionality as required by Protective Relay networks. Combining these two communication schemes in the same fiber ring with Self Healing capability enhances the reliability of network architecture at an optimized cost.

It will then be broadcast by the two Masters in each direction over the fiber. This process enables the fiber monitoring function of the Masters to protect the communications channels. In the event of a break in the fiber, the Communications channels will be recovered by the Self Healing operation of the network.