this.sensorTypes = {
  { label : "Power", value : "P"},
  { label : "Current", value : "C"},
  { label : "Voltage", value : "V"}
}

this.selectedAttributes = {
  {label : "Current", value : "C"},
  {label : "Voltage", value : "V"}
}

<div class="form-group row">
   <div class="col-sm-10">
     <ng-select [ngClass]="'ng-select'" [(ngModel)]="selectedAttributes" [ngModelOptions]="{standalone: true}" [options]="sensorTypes"
                [multiple]="true"></ng-select>
  </div>
</div>