Liebert 30-130kVA manual Operation After End-of-discharge, Battery Disconnect, Inverter

Theory of Operation

Operation After End-of-discharge

The battery time screen displayed on the control panel enables you to estimate when battery shut- down will occur. You will have enough time to energize an alternate AC power source or to initiate an orderly shutdown of the critical load. If the battery plant discharges to the shutdown point during an outage, the UPS automatically disconnects the load, the AC input, and the battery. After AC input power is restored, the rectifier can be manually restarted by the Operator.

Battery Disconnect

The module battery disconnect (MBD) circuit breaker is used to isolate the UPS module from the bat- tery during maintenance, and to automatically disconnect the battery from the inverter at the end of battery discharge. The MBD circuit breaker must be closed manually unless you have the optional motorized battery breaker. (See 3.3.8 - Auto Restart).

Battery Charge Current Limiting

The battery recharge current, after a battery discharge, is limited to between 1 and 25% (adjustable) of the full load maximum discharge current stated in AMPS. This regulates the amount of current that flows from the power source to the battery while the battery is recharging.

The battery charge current limit is factory set at one-half of maximum or 12.5% for normal operation and at 1% for alternate power source recharge operation.

Battery Equalize Charge Circuit

The battery equalize charge feature can be manually initiated or it can be programmed to operate automatically. Either can be selected from the battery equalize screen displayed on the control panel.

The automatic battery equalizing charge circuit increases the rectifier/charger output voltage to charge the battery anytime there is a power outage of 30 seconds or longer. The equalizing voltage is slightly higher than the float voltage. This helps all the batteries in a string to reach a uniform state of charge.

NOTE

The manufacturers of the valve-regulated batteries supplied with Liebert’s standard battery cabinets recommend that when first installed the batteries be equalize charged. After that initial equalize charge, they recommend no further equalize charging for their batteries. Other manufacturers may have different recommendations for their products. Consult the battery manufacturer’s manual for specific information about equalize charging.

2.2.4Inverter

The inverter is a solid state device that converts the DC output of the rectifier/charger or the battery to AC power.

Operation

The inverter converts DC power from either the battery or the rectifier/charger into three pulse- width-modulated/six-step waveforms. These waveforms are filtered into low-distortion sine wave power. The inverter is controlled by a Digital Signal Processor (DSP). This DSP controls the precise synchronization, amplitude, and frequency of the output voltage.

In addition to the inverter efficiently supplying a regulated AC output from a DC source, the inverter output provides isolation between the critical load bus and the commercial source power. The inverter is configured to handle most critical load inrush surges. It maintains output voltage Total Harmonic Distortion (THD) within specifications even when handling nonlinear computer loads.

Output Regulation and Overload Performance

The inverter is capable of sustaining full output voltage (±1% of the nominal voltage) for up to 150% overload at the output for as long as 60 seconds without reducing the output voltage. It can also han- dle at least 125% of the rated current for up to 10 minutes. If an overload exceeds the system capacity and a bypass source is available, the critical load is transferred to the bypass source and the inverter is disconnected from the load.

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