*3.2.3. Analyse the graph*

**3.** Analyse the graph.

136 Sustainable Energy - Recent Studies

processing.

*3.2.2. Log the current*

**4.** Convert the current to power.

*3.2.1. Measure the power factor at different loads*

draulic motors are running without any load, i.e., idling.

Active < 250 0,82

Idling 48 0,38

**Table 4.** Measured power and power factor for a hydraulic press.

**Figure 9.** The current used by a hydraulic press during one week.

**Mode Power (kW) Power factor, λ**

original current logging data is presented in a graph (Figure 9).

How to do this will be shown with measurements from a hydraulic machine for sheet metal

The power factor is measured while the machine is running. The machine has two well-defined modes of operation – one when the metal sheets are actually shaped and one when the hy‐

The current is logged for about a week, to cover working days as well as the weekend. The

**5.** Analyse the data again.

From the graph (Figure 9), it is clear that the machine is not used Friday to Sunday and for some hours during the nights. The machine is turned off during non-production hours. None‐ theless it has some idling power during the weekend and nights. The conclusion is that there are in fact three different modes to consider: active, idling and standby. The periods with zero current in the beginning and the end of the graph is the time before the logger was connected to the machine and after it was disconnected.

**Figure 10.** Duration diagram of the current used by a hydraulic press during almost one week (6,8 days). The active mode lasts for about 20 hours, the idling mode for about 1,5 day and the standby mode for about 4,5 days.

One way to analyse the graph is to create a duration diagram with the logged data, as in Figure 10. The duration diagram can be used to distinguish between the modes and to estimate the energy use for the different modes.
