BFM136 Application Note |
1. INTRODUCTION
One of the main issues that arise when addressing sub-metering projects is the retrofit issue. Many existing commercial buildings are interested in applying sub-metering solutions. At the same time, penetrating this market segment requires multi-channel capability to facilitate multi-tenant commercial sub-metering as well as retrofit wiring configurations support. This Application Note provides general hints about using the 3-phase multi-channel branch feeder monitor (BFM 136) for US commercial applications.
2. WIRING CONFIGURATIONS
2.1 Single-Phase Two-Wire
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The single-phase two-wire configuration is supported by the BFM136 feeder monitor. The device can provide sub-metering for up to 36 single-phase tenants. Unused voltage inputs should be shorted to the neutral (VN) input to avoid erroneous phase-to-phase and phase-to-neutral voltage readings. |
2.2 Two-Phase Three-Wire
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The two-phase three-wire configuration (see Fig. 2) is supported by the BFM136 feeder monitor. The device can provide sub-metering for up to 18 two-phase tenants. Unused voltage input should be shorted to the neutral (VN) input to avoid erroneous phase-to-phase and phase-to-neutral voltage readings.
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2.3 Three-Phase Three-Wire Delta
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The three-phase three-wire Delta (no neutral) configuration is supported by the BFM136 feeder monitor. The maximal phase-to-phase voltage allowed for the BFM136 device is 480V (tested by SATEC Ltd). The device can provide sub-metering for up to 12 three-phase tenants, for three-phase applications only. The phase to neutral voltage readings for this wiring configuration has no physical meaning and should be disregarded. Certainly, these readings do not affect energy metering. |
2.4 Three-Phase Four-Wire Delta ("Red Leg" Delta)
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The three-phase four-wire Delta ("Red Leg" Delta) configuration is supported by the BFM136 feeder monitor. The neutral (VN) input must be connected to the ground of "Red Leg" Delta. The maximal phase-to-phase voltage allowed for the BFM136 device is 480V (tested by SATEC Ltd). The device can provide sub-metering for up to 12 three-phase tenants. |
3. Multi-channel sub-metering
3.1 Basic Principle
Fig. 5. Schematic circuit demonstrating basic principle of multi-channel sub-metering by BFM136 branch feeder monitor
Figure 5 shows schematic drawing (example) of multi-channel BFM136 connection. Figure 5 demonstrates basic principle of multi-channel (multi-tenant) sub-metering by use of the BFM136. Voltage inputs are common for all channels. Same voltages must be supplied to all tenants. Otherwise sub-metering is not supported by the BFM136. The current inputs of BFM136 are fed from external CTs according to a number of phases provided to a specific tenant (1, 2, or 3 CTs per channel). Up to 36 current channels can be monitored by the BFM136. As a result, up to 36 one-phase tenants, up to 18 two-phase tenants, up to 12 three-phase tenants, or any combination of those.
3.2 PAS channel assignment
Fig. 6 Channel assignments for multi-tenant sub-metering by use of PAS SW
Fig. 6 depicts channel assignment settings to be performed by the PAS software. One can clearly see that Tenant #1 is two-phase (I1 and I2 current inputs are assigned to the tenant), Tenant #2 is one-phase (I3 current input is assigned to the tenant), Tenant #3 is also one-phase (I4 is assigned to the tenant), etc.1 The channel assignment menu is approached by entering to Meter Setup / General Setup / Channel Assignments.
1. Important Note: For proper energy sub-metering all tenants must use the same line voltage since a single voltage input for all channels is implemented in the BFM device.
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